That EPC light.

The most likely reason you're reading this blog post, is because you encountered an EPC fault with your Volkswagen vehicle. I bet you wondered what that yellow/orange light was when it lit-up or perhaps startled when you car went into "limp mode". Whether you're driving a VW Polo or VW Jetta, VW Golf,  VW Caddy, VW Passat, T-Cross, Sharan, Touareg, Transporter, or any other Volkswagen or even a German Audi, or a Czech Skoda or a Spanish VW SEAT, you've come to the right place because they all have an  Electronic Power Control circuit. 

In fact all "modern day" vehicles have EPC circuit, which loudly says that the automotive industry have finally reached some consensus on standardization. But let me tell you what the EPC light actually is. It's just a signal light informing you that there is an error in your vehicles torque circuit. That's the short answer, however, I can tell by the look on your face that it wasn't a  satisfactory answer, so let me give you the long version.

The EPC light is part of the Electronic Power Control Circuit which is just one of the components of OBD-II which was mandated by a certain regulatory bodies with regulatory intent. Their initial intention was to limit carbon emissions / exhaust fumes from cars on the street of America. 

The California Air Resources Board (CARB) and the Environmental Protection Agency (EPA) together with the Society of Automotive Engineers (SAE) and the International Organization for Standardization (ISO) collectively originated the On-Board Diagnostic (OBD) System because of high levels of smog produced by automobiles throughout the USA.  

Their initial On-Board Diagnostic System was subsequently superseded by the all new and improved verion OBD-II, hence all cars manufactured post 1996 has an Electronic Power Control Circuit and by extension an EPC light. The European on-board diagnostics (EOBD) regulations are the European equivalent of the American OBD-II. 

On-Board Diagnostic (OBD-II) is an automotive mechatronic, micro processor / micro controller based computer system with programmed presets that continuously monitors inputs from numerous sensors fitted through the car. 

It then computes/compares/ compensates these inputs against stored data and drives various actuators to perform certain tasks. In a nutshell OBD-II is an input/output (I/O) information processing system much like the PC / laptop / or even your smart phone. By example, a keyboard, a mouse, a joystick, a scanner and a microphone are common computer input devices whereas a HD monitor, a printer, speakers and headphones are common computer output devices. 

Here the computer/laptop makes calculations based on its internal operating system and software to do something intelligible for humans. However in the case of OBD-II, its CPU (Central Processing Unit) is called an ECU (Electronic Control Unit) and among its input sensors are the Accelerator Position Sensor, Mass Air Flow sensor (MAF), Lambda O2 Sensor, Knock sensor, Oli level sensor, Coolant Temperature Sensor, the Camshaft Position Sensor, the Crank Position Sensor, the Wheel Speed  Sensor etc, to mention but a few.

Among its output actuators and solenoids are the drive-by-wire electronic throttle actuator, the fuel injectors, the EPC light, Malfunction Indicator Light (MIL), the Immobilizer, the Airbags and the Power Steering Pump, etc, again to mention but a few,

This ECU is sometimes referred to as an Engine Control Unit especially when intending to make reference to the TCU (Transmission Control Unit). The ECU is sometimes even called ECM (Engine Control Module) when making reference to other electronic control modules like the ABS module, the Instruments module, the Central Electronics Module, the CAN gateway module, the Radio Module, etc, again to mention but a few 

However, the ECU and the TCU are collectively referred to as Powertrain Control Module (PCM). The ECM essentially controls the efficiency of the engine performance by using a Crankshaft Position Sensor to determine the position of the cams in order to activate the injection of fuel into the cylinders and the timing of the ignition spark to ignite it at precisely the correct moment in petrol engines. 

Likewise the ECM in Diesel engines, plays a huge role in the success of the turbodiesel models. But in order for this to happen, an electronic throttle control had to be introduced, replacing the  cable from the pedal to the carburetor system which was prone to idle speed deviation between a hot and cold engine that became more and more prevalent as the components wore out. 

In so doing, the ECM can adjust the electronic throttle angle during acceleration to achieve the right quantitative relationship ratio between the actual airflow through the engine and the injected fuel thus maintaining Stoichiometry. Controlling the throttle airflow on the fly, markedly improves overall torque and driveability which is known as torque-mapping, an advantage that is only possible with drive-by-wire. 

So, the Electronic Power Control Circuit consists of the ECM, the Accelerator Position Sensor, the Throttle Position Sensors, the Throttle Actuator, the MAF / Air Filter, the Fuel Injectors, the High Pressure Fuel Pump, Fuel Temperature Sensor, Fuel Rail Pressure Sensor and Pressure Relief Valve. 

The single accelerator position sensor is made up of two individual potentiometers each acting independently of the other but collectively operate with opposite polarity voltages supplied by the ECM, as a safety back-up for one another. 

Thus, if either potentiometer fails, the ECM will activate limp mode. This is a safety measure that prevents the system from acting as if it had an accelerator cable that got stuck in the runaway position and the makings of a potential accident. The cruise control also has influence on the throttle body and requires the brake pedal to be depressed to cancel the cruise control. 

The ECU normally takes this cancellation signal from the brake light MOSFET low-side driver in the ECU. So either the brake pedal switch and the a brake light bulb can cause an EPC error along with the aforementioned fuel supply components. It's best to have a diagnostic tester to check for DTC errors via the DLC connector. It would at the very least steer you in the right direction to fix your EPC problem effectively.

Electronic Power Control (EPC)

It was very surprising to discover how many thousands if not millions of car owners out there, have no idea exactly what  Electronic Power Control (EPC) is. Yet most of them would like to know what the Electronic Power Control (EPC) circuit really does , more especially the Volkswagen, Audi, Seat and Soda owners. 

Considering they've been plagued by the Electronic Power Control (EPC) light, limp mode, DTC errors and poor engine performance to the point of frustration and panic for a number of years. Nobody seems to be able to give them good advice or practical guidance; and in many cases not even the Volkswagen, Audi, Seat and Skoda agents can. 

Leaving VW owners confounded, disappointed and disillusioned by their choice in cars, which results in so many car owners swearing, never to invest in VW brands ever again.

Unscrupulous motor mechanics tend to take advantage of these situations, recommending that the car owner brings their car to them as soon as possible before damage occurs to the engine.  Whereas in fact, the Electronic Power Control (EPC) is a safety circuit designed to prevent damage to the engine. 

When the  Electronic Power Control (EPC) mode does engage, it can and often does affect the car's stability and cruise control and torque circuit giving the impression there is a lot more wrong than there actually is. 

Since the Electronic Power Control (EPC) is "yellow" and not red, it acts more as an advisory light rather than a warning light, even though everybody tends to call it a warning light. A  flashing amber light is considered a "warning signal" but still doesn't have the danger status of "red warning light". 

 


Technically the "yellow" Electronic Power Control (EPC) light is in fact  amber which is a blend between orange and yellow. Car dashboard light colours can be roughly divided into three categories. 

Warning lights are Red in colour. Advisory lights are  amber in colour and information lights are generally either white, green or blue in colour. Having said that, its simple to understand that amber implies that you should keep an eye on, or be prepared for either  a reduction in power or  interruption to power.

Hence, Amber lights are used as Indicator lights (flashers) on cars for the turn signal and hazards. Amber lights are also used by roadside breakdown vehicles to alert drivers. An amber traffic light is generally considered a cautionary light, signalling  readiness to stop. Much like an amber  traffic light does. 

Now that you know what the colours of the lights imply, allow me to give you the low-down on Electronic Power Control (EPC) itself. EPC is an acronym and it is the official abbreviation for Electronic Power Control. 

Electronic Power Control is an embeded system, specifically designed into electronic circuits that permits it be part of a larger electro-mechanical system.  An Electronic Power Control system can also simply be described as a self-contained "feedback" circuit.  

It can even be further  explained, as a microprocessor based electronic circuit -or a computer if you like- that alters its output bias based on its inputs. Its "status quo" or current baseline is taken as a reference point and the objective is to control its operation within its predetermined parameters, and as close as possible to the said baseline, based on the signals from its inputs. 

Should any of these inputs, that predominantly come from sensors fail, for whatsoever reason, the computer circuit wouldn't be unable to complete its processes and would either enter into a "compensatory state", a "warning state" or an "error state". But more about this later!

The Electronic Power Control circuit has become standard equipment as part of the OBD-II (On-board Diagnostics 2) system in all modern day cars, manufactured since 1996. The Electronic Power Control is an integral part of every computerized ignition and engine management system, embedded into the ECU (elcectronic computer unit). 

The Electronic Power Control (EPC) dashboard advisory light is also part of this system and is normally activated by errors in the vehicle's torque circuit but not exclusively. The Electronic Power Control (EPC) light is  actually  a "new" addition to the plethora of light on the more modern vehicle's dashboards, a light  that gives any driver a sense of despair when it turns on. 

But more about that later ...

However, since a full blown explanation is outside the scope of a single blog-post, it is imperative that you need to read  every blog installment or the entire blog to get the full Electronic Power Control (EPC) picture.

____________________________________________________________________

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Annoying VW EPC light

VW EPC expounded

As I've explained in an earlier blog, the amber Electronic Power Control warning light on your car's instrument cluster, is just an indicator light; drawing your attention to either (1)  an Auto-Correct EPC Problem, (2) a Pending EPC Problem, (3) an Existing EPC Problem or  (4) a Current EPC Problem. 

An Auto-Correcting  EPC problem occurs when the EPC light goes on without noticeable difference in engine performance and goes off during subsequent drive cycles which may be within a day or two or longer.

A Pending EPC Problem could be something as simple as a spark plug misfiring intermittently and appears in the scan list but after a while becomes an Auto-Correcting EPC problem alternatively if the plug continues to misfire it becomes and Exising EPC problem.

An Existing EPC Problem could be something like the MAF sensor or a accelerator pedal sensor that needs cleaning or replacement and a Current EPC Problem normally results in limp mode.

EPC light is bright YELLOW/AMBER and acts as a indicator, it is not as a warning light. 
Warning light are always RED.

EPC light is bright YELLOW/AMBER and acts as a indicator light, an advisory light; it is not as a warning light.  Warning light are always RED. Since the ECU "learns your driving style" over time, it records your optimize drive cycles to non-volatile memory along with atmospheric pressure, min & max rpm and the average fuel use data, etc, then creates an adaptive pattern or map based on these parameters. 

When this map is compared to sudden spirited driving, it may trigger the EPC light but will auto-correct (reset) itself after a few driving cycles within a day or two. Sometimes the EPC light may be accompanied by the Check Engine Light (CEL).

A Pending Problem can cause the EPC light to come and not switch off on its own. Pending implies that the problem will only get worse if left unattended to. A diagnostic scanner is needed to view the DTC error, hence its really worthwhile investing in one. 

For example, assume that cylinder number 3 randomly misfired a few times as the pending problem. The scan freeze frame data will show something like this.

000771 - Cylinder 3

               P0303 - 000 - Misfire Detected - Intermittent

             Freeze Frame:

                    Fault Status: 00100000

                    Fault Priority: 2

                    Fault Frequency: 7

                    Reset counter: 255

                    Mileage: 38187 km

                    Time Indication: 0

                    Date: 2021.11.05

                    Time: 21:09:58

             Freeze Frame:

                    RPM: 758 /min

                    Load: 13.1 %

                    Speed: 0.0 km/h

                    Temperature: 51.0°C

                    Temperature: 33.0°C

                    Absolute Pres.: 830.0 mbar

                    Voltage: 12.435 V

What this means is that cylinder misfired 7 time, and that the most recent misfire occurred at the displayed time and date highlighted in red and has a fault priority of 2.  Fault priority of 4 or lower needs to be attended to immediately since it affects the driveability of the car. Don't ignore the VW EPC light.  

Fault priority of 5 and above doesn't require immediate attention but must be attended to sooner rather than later. The freeze frame date shows that the car was idling and 758 rpm with the speed at 0 kph and that the engine hasn't reach its optimum operating temperature as yet. In a nutshell, freeze frame captures the engine operating conditions at the time when the EPC error occurred.

An Existing EPC Problem could  mean either the throttle pedal, throttle body, or brake control unit or any other circuit related to the torque circuit, like the  cruise control unit or the traction control unit is misbehaving.  However the EPC light can also indicated an unrelated problem like a loose fuel cap. With the EPC light on, and a pungent fuel smell inside the cockpit would point you to fuel cap.  

Since the fuel is under pressure, the fuel pump, fuel regulator or fuel rail pressure sensor may also be suspect, each should be excluded through a process of elimination. Remember the Electronic Power Control system is integrated with several other systems on you vehicle, like the steering control unit and the ECU, hence it's not always easy to diagnose.

Its permissible to  drive your VW for a short distances and for a short period of time after the EPC light has triggered, that's to say if driveability hasn't been impaired but its best to either fix it yourself or take it to  VW service center. An  EPC dashboard light can be caused by any of the following, but in no particular order. Sometimes both the EPC light and CEL (check engine light) would turn on.

1) Brake Light Switch failure

2) Mass Air Flow Sensor failure 

3) Engine Speed Sensor failure 

4) Throttle System Potentiometer Failure

5) Cruise Control failure

6) Accelerator Pedal Potentiometer failure

7) Repeated cylinder misfires

8) Loose fuel cap

9) Blown / Faulty  brake light

Any of these can and may cause your vehicle to go into “limp mode” which can be described as a Current EPC Problem. When limp mode strikes, the Engine Control Unit will limits the functions of the torque circuit and transmission thus prevent your VW's engine from  revving higher than 2000 rpm and limit its speed to 30-45 kpm. 

Some mechanics would reset the EPC light by cleasing the DTC list without fixing the actual problem but this is not recommended. When the  Diagnostic trouble codes (DTC) are cleared,  "your driving style" map is also deleted, meaning that the ECU would have to relearn  "your driving style"  from scratch and your VW's performance may seem a bit off.  That's to say, until your racked up sufficient drive cycles (data) with which the ECU can do an analysis in real time. 

Grand Theft Auto

Volkswagen (VW) motor vehicles are not only popular among car enthusiasts, they  are also very popular car among the first-time car-buying youth. That said, VW vehicles have also become most popular car among car thieves to steal.

According the Crime Statistics Report for the years 2020 and 2021 - released by the South African Police Service (SAPS)- motor vehicle theft in general has steadily increased since 2011. However, it is correct thinking to assume that thieves have a preference to certain make and model of car.  Case in point - both the VW Polo hatchback and VW Polo sedan are at a higher risk of being stolen than any other VW model and other manufacture's vehicles as a whole.  

VW Polo Hatchback

Since its release in 2018 the VW Polo Hatchback had become the most stolen cars in South Africa. By 2019 it was the most sold passenger vehicle; targeted by "chop-shops" -illegal garages that buy stolen cars - to disassemble them and sell their individual components for profit - aka midnight spares. 

The new VW Polo hatchback - front-wheel drive, 5 door with 5 seats, powered by a 2.0L TURBO 4 engine that outputs 147 kW of power and 320 Nm of torque costs roughly between R320K and R480K whereas a older model or one with  a lower capacity can sell for anything from R170 000 and R250 000 subject to millage and overall condition.

VW Polo Sedan

The VW Polo sedans comes in as either Trendline, Comfortline, Highline and are essentially the sedan version of the  VW Polo hatchback with and engine capacity of either 63 kW  of 77kW fetching a price between R270k and R350k.

Insurance

Loosing a vehicle of this calibre with such a pricetag can be really gruesome hence a condition of any hire-purchase agreement to keep the vehicle adequately insured but an anti hijack immobilizer and alarm system is also essential. Car insurance coupled to Life Insurance may also be highly advantagious.

Anti-theft Alarm, Remote Central Locking and Remote Central Locking are not standard features of all models but the all do come with an Immobilizer but without Automatic Door Lock. It is therefore feasible to invest in an anti-Blocker, anti-Signal, anti-Jammer engine immobilizer with vehicle tracking GPS tracker support and engine cut in preference of the factory fitted product.

Transponder detection

Since most later vehicles are fitted with receiver and transponders chips, stealing a car without having its corresponding key is quite difficult.  If the key isn't close to the steering column stalk that houses the receiver coil or not within key detection distance then engine will not start.  Thieves also resort to key re-programmers and signal grabbers to counteract new technologies like ‘push to start’ buttons installed in the later model vehicles.

Carjacking

So, in order for thieves to steal your car they would have to take it from you by force  - hijacking, a horrific experience. Most cars today are stolen that way by hijacking the driver. If the thieves don't have the matching ignition key, the immobilizes prevents them from starting it by inhibiting the starting process, hence they take the car from the driver with key by force -carjacking. 

Safety Tips to prevent a possible hijacking

Before getting into your car, look around for any any suspicious characters. Should they be around alert a friend, family member or neighbour, even get them to accompany you.

Hijackings are often than not planned, so be be vigalent and cognizant of vehicles following you even at a distance.

Jot down the number plates of vehicles that or that continually pop up on your daily travels and check against previous ones.

Report any s suspicious activity to your local neighbourhood watch or security company of police.

Make sure that you are not being followed before driving into your driveway where you could be cornered.

Alert someone at home before driving into your driveway, to come outside to observe if there are suspicious characters lurking about.

Always be aware and alert of your surroundings before getting out of your car.

Never stop or park your car in a way that you cannot get away from someone following you quickly. 

Be aware of any vehicle blocking your driveway as you pull into it. Honk your hooter constantly to alert neighbours. It may be sufficient to scare them off.

The Most Common Car Problems

There was a time when car owners could easily service their own cars. Simply replacing points, plugs and condensors,  draining its oil and replacing its oil and oil filter normally put the car back on the road again. Those were the days when the most common roadside problem was a puncture or a snapped fan belt. Punctures were easily fixed with a replacement tyre from the trunk. All that was needed was some elbow grease applied to the jack, wheel brace and wheel nuts and you were on the road again. But today rollbacks are are integral part of motoring. Hundreds of cars are loaded up everyday on the road side.

The main cause of punctures was attributed to poor road surfaces, random metal objects and broken glass and to a lesser degree older tyre technology. Even though punctures were predominant, they were by no means exclusive to roadside breakdown because clutch plates and gearbox problems were also plentiful, as was running out of fuel.

With the advent of newer cars, the race for the most fuel efficient and least expensive car was on. When fuel and air stoichiometrics were at its peak, car manufactures started producing cars with a 'Space Saver Biscuit Spare Wheel' which took several kilograms of weight out of the trunk, This made the car a tad lighter, slightly more fuel efficient and ever so slightly, cheaper to produce.

Today, almost a third of all new cars don't even have a spare wheel; instead they may be equipped with a can of self inflating puncture-repairing foam, or an electrical air compressor with some sealant kit to temporarily fix a flat tyre. Both options are evidently cheaper than a Space Saver Biscuit Spare Wheel and lighter.

However, believe-it-or-not, the more expensive cars today, are sold without  a spare wheel, instead they are fitted with “run-flats”. In a nut-shell, run flats are special pneumatic tyres, designed to resist the effects of deflation when punctured, yet enables the car to  be driven at reduced speeds of under 90 km/h for a distance of up to 80 km. The speed and distance of course to the nearest tyre repair shop, is subject to the type and quality of the “run-flats”.  So, once again the manufacturer saves the cost of supplying a spare wheel.

Be that as it may, snapped fan belts  often causing the engine to overheat, sometimes resulted in a  blown  cylinder head gasket. Subsequently, the modern day electric radiator fan has totally supperceeded the belt driven fan and as a result, burst radiator hoses, corroded, leaking water pumps and welch plugs have  became the primary cause  of blown cylinder head gaskets. The other bugbear is oil leaks that weren't timeously attended to, currently trending as the most common cause of seized engines. 

With the abundance of electronics fitted into cars, the alternator  and its voltage regulator have  became a lot more more troublesome than ever before. Obviously due to the additional electrical load.  Alternator  problems are closely followed by starter issues when either its brushes or its  bendix reaches its end of life.   

Both types of problems have resulted in batteries being replaced prematurely and sometimes unnecessarily. Brakes and Turbos also give their fair share of problems, but none of these problems comes close to the new type of roadside breakdowns caused by the OBD-II system.

The most common cause of  breakdowns today, is the Electronic Power Control (EPC) light; not that the light is the cause of the problem. The Electronic Power Control (EPC) light is only an advisory light, drawing your attention to a possible malfunction or  pending problem or  already existing problems.

When the Electronic Power Control (EPC) light comes on, without the ESP or Check  engine light, the car is normally still driveable, even if it goes into limp mode. But when accompanied by the ESP and or CEL (check engine light) the car may refuse to start as its inhibited by the Electronic Computer Unit (ECU). 

When this happens, the only solution is to secure a rollback to fetch the car and take it either to your service agent / mechanic or your home, so that you can tend to the problem yourself. 

There is no way you'd be able to effect repairs to your car yourself without a OBD II scanner   that would direct you to, or confine your repair to a certain area of the engine. 

Below are a few sample yet partial ODB II diagnostic scans  for Electronic Power Control (EPC) problems. 

This for a 7N0 - VW Passat.
Address 01: Engine (CDL)       Labels: 06F-907-115-CDL.clb
   Part No SW: 1P0 907 115 AB    HW: 8P0 907 115 B
   Component: 2.0l R4/4V TFSI     0020  
   Revision: 5BH20---    Serial number: 0000              
   Coding: 0303004C18070160

1 Fault Found:
008487 - Accelerator Position Sensor 2 (G185) 

               P2127 - 002 - Signal too Low

Electronic Power Control (EPC) problem  for a 1J - VW Golf.

Address 01: Engine Labels: 06A-906-032-AWP.lbl

Part No: 06A 906 032 RN

Component: 1.8L R4/5VT G 0001 

Coding: 07510

18047 - Accelerator Position Sensor 1/2 (G79/G185) 
            P1639 - 35-00 - Implausible Signal
18042 - Accelerator Position Sensor 2 (G185) 

            P1634 - 35-10 - Signal too High - Intermittent

Electronic Power Control (EPC) problem  for a 7L - VW Touareg 

Address 02: Auto Trans        Labels: 09D-927-750.lbl
   Part No: 09D 927 750 AN
   Component: AL 750 6A           0546  
   Coding: 0004153


1 Fault Found:
00777 - Accelerator Position Sensor (G79) 

            004 - No Signal/Communication - MIL ON

NB! The Automatic Transmission module and not the Engine Module detected this accelerator sensor problem.

 

Electronic Power Control (EPC) problem 1H - VW Golf/Vento III
Address 02: Auto Trans       Labels: 01M-927-733.LBL
   Controller: 01M 927 733 CT
   Component: AG4 Getriebe 01M    3363
   Coding: 00000
    

1 Fault Found:
00518 - Throttle Position Sensor (G69)

            16-10 - Signal Outside Specifications - Intermittent

NB! The Automatic Transmission module and not the Engine Module detected this accelerator sensor problem. Here the Throttle position sensor instead of the Accelerator sender is the cause of the problem.

Electronic Power Control (EPC) problem  for a 9M - VW Jetta IV.
Address 01: Engine Labels: 06A-906-032-AWP.lbl
Part No: 06A 906 032 RN
Component: 1.8L R4/5VT G 0001 
Coding: 07510

1 Fault Found:
18047 - Accelerator Position Sensor 1/2 (G79/G185) 

P1639 - 35-00 - Implausible Signal 

Electronic Power Control (EPC) problem  for a 8E - Audi A4.
Address 01: Engine Labels: 06C-909-559-ASN.lbl
Part No SW: 8E0 909 559 D HW: 8E0 909 059 
Component: JHM V3/9X G 0003 
Coding: 0016751

2 Faults Found:
18047 - Accelerator Position Sensor 1/2 (G79/G185) 
P1639 - 008 - Implausible Signal - Intermittent
18047 - Accelerator Position Sensor 1/2 (G79/G185) 

P1639 - 008 - Implausible Signal - Intermittent - MIL ON

Electronic Power Control (EPC)  for a 8P - Audi A3.
Address 01: Engine Labels: 06A-906-033-BGU.lbl
Part No: 06A 906 033 DS
Component: SIMOS71 1.6l 2V 5559 
Revision: --H03--- Serial number: AUX00000
Coding: 0000071

4 Faults Found:
18047 - Accelerator Position Sensor 1/2 (G79/G185)

P1639 - 008 - Implausible Signal - Intermittent

Electronic Power Control (EPC) problem  for a 9M - VW Jetta IV

Address 01: Engine Labels: 06A-906-032-AWP.lbl

Part No: 06A 906 032 LP

Component: 1.8L R4/5VT G 0005 

Coding: 07500

18042 - Accelerator Position Sensor 2 (G185) 
P1634 - 35-00 - Signal too High
18039 - Accelerator Position Sensor (G79) 

P1631 - 35-00 - Signal too High

 Electronic Power Control (EPC) problem  for a 1C - VW New Beetle

Address 02: Auto Trans Labels: 01M-927-733.lbl
Part No: 01M 927 733 EN
Component: AG4 Getriebe 01M 4108
Coding: 00000

1 Fault Found:
00518 - Throttle Position Sensor (G69)

16-10 - Signal Outside Specifications - Intermittent

NB! Once again the Automatic Transmission module  detected this Throttle position sensor instead of the Engine Module detecting the Accelerator sender to be the cause of the problem.

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As can be seen from the data above,  there are essentially 3 types of  DTC errors responsible for triggering the EPC light, though not exclusively. P codes  P1630 and P2122;  P1631 and P2123;  P1632 and P1861 are essentially the same and applies to sender 1. 

As can be seen below.
P1633 and  P2127;  P1634 and P2128; P1639 and P2138 are essentially the same but applies to sender 2. There are also several other DTC errors that can and trigger the EPC and or along with the ESP, and or with the CEL.

Accelerator Pedal Sensor 1

P1630 - Accelerator Pedal Pos. Sensor 1 (G79), Signal too Low

P1631 - Accelerator Pedal Pos. Sensor 1 (G79), Signal too High

P1632 - Accelerator Pedal Pos. Sensor 1 (G79), Power Supply Malfunction

P2122 - Accelerator Pos. Sensor 1 (G79), Signal too Low

P2123 - Accelerator Pos. Sensor 1 (G79), Signal too High

P1861 - Accelerator Pos. Sensor 1 (G79), Error Message from ECM

Accelerator Pedal Sensor  2

P1633 - Accelerator Pedal Pos. Sensor 2 (G185), Signal too Low

P1634 - Accelerator Pedal Pos. Sensor 2 (G185), Signal too High

P1639 - Accelerator Pedal Pos. Sensor 1/2 (G79) / (G185), Implausible Signal

P2127 - Accelerator Pos. Sensor 2 (G185), Signal too Low

P2128 - Accelerator Pos. Sensor 2 (G185), Signal too High

P2138 - Accelerator Pos. Sensor 1/2 (G79) + (G185), Implausible Signal

Throttle Position Sensor

16505/P0121/000289 - TPS (G69): Implausible Signal
16506/P0122/000290 - TPS (G69): Signal too Low
16507/P0123/000291 - TPS (G69): Signal too High

Throttle Angle Sender 1

17950/P1542/005442 = Angle Sensor 1 for Throttle Actuator (G187): Implausible Signal
17951/P1543/005443 = Angle Sensor 1 for Throttle Actuator (G187): Signal too Small
17952/P1544/005444 = Angle Sensor 1 for Throttle Actuator (G187): Signal too High  

Throttle Angle Sender 2

16605/P0221/000545 - Angle Sensor 2 for Throttle (G188): Signal   Implausible 
16606/P0222/000546 - Angle Sensor 2 for Throttle (G188): Signal Too Low
16607/P0223/000547 - Angle Sensor 2 for Throttle (G188): Signal Too High

Depending on the model of your vehicle, its Throttle position sensor (TPS) lowest output voltage should be around .17 Volt and when the Electronic Control Unit (ECU) detects that it has dropped below that, then it will trigger either a P0122 or P0222 code.  High signals are not common but they do occur. 

 

As can be seen from the above data the error signal is either too low or to high or intermittent/implausable. Bearing in mind that a constant 5 volts is supplied by the ECU via a High-side or Low-side driver to the each of these potentiometers (senders). Loss of the voltage or even intermittently loss will trigger the EPC light and enter into "limp mode".

By implication  the monitored output is in 1 of 3 states, viz, low, high, or intermittent. In order to determine these states, the ECU needs a reference to compare these signals against. Each sender therefore act as a reference for another and any discrepancy between the two can result in an EPC error and subsequent limp mode. 

Replacing the Accelerator Pedal sensor (potentiometer)  unit normally fixes the EPC problem, but limp mode can also be caused by the throttle butterfly potentiometer.  And like I mentioned before, an OBD-II diagnostic tester would make this repair a lot easier and a lot faster.


NB! When your car goes into "limp mode", you may have  a lit   "Engine Management Light" (EPC icon) and or a "Electronic Stability Light" (skidding car icon) and or a "Engine Control Lamp" (engine icon) or any other combination thereof.  

Even Earthworks machinery are fitted with OBD-II so that exhaust emissions can be controlled but when there is a problem in the OBD-II system, invariable these machines would have to go on a roll back and taken for repair.

 

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What your Electronic Power Control (EPC) Warning Light really means

Computers are ubiquitous or rather microcomputers, microprocessors and their peripheral systems and chipsets are.  As such, they can be found in most electronic devices, ranging from laptops to printers, routers, radios, walkie-talkies, cell-phones and toys to mention but a few. In fact, microprocessors are so common place that they've taken over most hand held and personal electronic devices so-much-so that they are even embedded in our entertainment equipment, our cars, motorcycles, aeroplanes, ships and trains. It can thus be said that electronics in all its technological forms, have completely changed how we live  our lives. These systems along with its sensors, sendors and actuators are referred to as On-Board Diagnostics (OBD) and since it's in its second revision, known as OBD-II or just OBDII.

Furthermore  these On-board diagnostic (OBDII) digital computers interfaced with its dependency modules, electro-mechanical systems and sensors built into our cars have collectively taken-over and superseded most mechanical linkage functions, that were previously and traditionally used for acceleration, steering control and parking brake among several other.  So, welcome to the world of  drive-by-wire, (electronic throttle control) steer-by-wire, shift-by-wire, brake-by-wire and fly-by-wire which is currently widely used in aviation. 

What your Electronic Power Control (EPC) Warning Light really says!

Your car's EPC light essentially indicates that there is an issue with the  torque system of your vehicle. This torque system is your car's acceleration and braking system that now operates via drive-by-wire, shift-by-wire and brake-by-wire. In a nutshell, it's a computer chip supervised electronic system (ECU) that replaced the cable linkage previously situated between the carburetor and the accelerator pedal with an electrical/electronic interface. 

This amber EPC light is an advisory light rather than a warning light -since warning lights are red in colour- is illuminated when the ECU detects a glitch in the torque system. When a glitch is detected, in most cases the ECU will enable 'limp home mode'. Limp mode is a fail-safe software-embedded, security and safety feature that  inhibits the system, activates a  rev limiter, shuts off boost partially or completely, resulting in a maximum 2500 RPM.  

Thereby leaving only sufficient power to safely drive the car home in some cases. In other cases it could prevent the car from even starting.  Limp mode also acts as a safe-guard against further engine / transmission trouble or possible runaway.  Switching off the engine and disconnecting the battery may in some cases momentarily cure limp mode, but then again it may not due to the ECU's  non-volatile memory. However as an  advisory light, it begs for an OBD-II diagnostic scan, so that the Trouble Code (DTC) error may be diagnosed and repaired. This is best done sooner rather than later, as Limp mode sometimes manages to cures itself, yet bound to repeat itself continually until repaired. The ECU has a counter / timer monitoring how many times the same DTC was detected since the last start-up. If just a few times (considered negligible / mistakenly triggered) the counter resets itself and starts to recount from when it happens again.

Having said that, EPC lights and drive-by-wire systems aren't exclusive to "VAG cars" like most mechanics would have you to believe. The EPC light is a mandatory part  of the OBD-II system hence fitted as standard equipment on "all post '96 cars". OBD regulations are written into Government legislation globally so that in time, the Department of Transport (DoT) may require all vehicles to regularly go for mandatory carbon emission tests in order the achieve road roadworthiness. They will access your cars under dash 16 pin obd connector to check its "Readiness Status". Readiness is an 2 x 4 digit binary number (hexadecimal) that look something like 1011 0110 or 1110 0101 or 0000 0000 or any combination of zeros and ones which is subject to the workings of equipment fitted in your vehicle.

Anyway, if you don't know, VAG stands for Volkswagen AG. The AG is an abbreviation for Aktiengesellschaft - implying incorporated. Aktiengesellschaft is the German term for a Public Limited Company (PLC). Thus the  VAG group is comprised of ten car brands  viz, Volkswagen, VW Commercial vehicles, Volkswagen Marine, Audi, SEAT, CUPRA, ŠKODA, Lamborghini, Porsche, Bentley and Ducati, spanning across five European countries.  In a nutshell most if not all these vehicles have a EPC light and torque control circuit operated via drive-by-wire as standard equipment. But as mentioned previously, an EPC lights with drive-by-wire and brake-by-wire is not exclusive to VAG cars.  

This torque circuit (throttle-by-wire) is a collection of interconnected electronic components amongst which are the car's battery, ignition switch, throttle body position sensor / potentiometer and throttle body actuator / stepper motor. The ECU itself, the braking system sensors and the wiring harnesses that supplies voltage / earth and feedback to and from the accelerator position sensor/ potentiometer and the throttle body motor, the cruise control switch, the instrument cluster and even one of the brake globes itself.

Possible problems

So by implication, with so many points of failure, so much can go wrong, For example, a loose battery terminal could cause the accelerator potentiometer input voltage to momentarily disappear for a fraction of a second, thus detected by the ECU which  would then trigger limp mode. It could also be caused by a speck of dust has settled on the potentiometer slider that creates a brief intermittent contact. The ECU will however detect this and implement limp mode. 

Then there is the dozens of wiring harnesses with their hundreds of connections. Several of them instrumental in the automotive torque circuit. Since electronics has taken over our cars, some having more than 3 dozen individual harnesses, collectively  comprising of more than 3000 wires and a third as many connectors. It gives you an idea of multitude of electrical problems that can occur.

Male and female wiring harness connectors used in the automotive industry are fairly reliable however due to the under-bonnet conditions like extreme engine heat and morning freezing temperatures, humidity, steam, condensation, oil splatter, dust and vibration, can collectively give rise to corrosion inside wired plugs and sockets. Corrosion normally causes high resistive electrical conditions which upsets the functionality of the circuit concerned.  

This could cause a myriad of problems in a myriad of circuits among which could be the MAF circuit, causing poor driveability and sudden jerking motions during acceleration flanked by untimed detonations.  It could be the MAP circuit causing poor fuel economy and difficult starting and rough idling. Catalytic converter wiring would cause dark exhaust smoke that  smell like rotten eggs due to the excess sulphur and the engine performance will be sluggish..... etc. Wait for the follow-up!