Electronic Power Control

Electronic Power Control

What Does the Electronic Power Control (EPC) Warning Light Mean?

Traditionally hand brake, accelerator pedal, clutch and bonnet release, used some sort of cable system and the steering column and gear levers used several mechanical linkages. Today virtually all these mechanical systems have been replaced by electronics in the form of sensors, feeding computers and electric motors performing as actuators. The legacy accelerator cable that controlled the throttle valve and fuel supply in the trusty old carbureter has been entirely replaced by electronics. It is now referred to as drive-by-wire (drive the car by means of electric wire control) and the EPC circuit oversees drive-by-wire system.

So what is an EPC circuit?

EPC stands for Electronic Power Control (EPC) and is a sub circuit of the car's computerized engine management system better know as its ECU which stands for Electronic Control Unit or  Engine control Unit. The EPC circuit uses the input signal supplied by the accelerator position senders and  the throttle angle senders to calculates how much engine power the driver requires. The EPC system also receives input signals from other systems on the car, like the stability and cruise control systems and translates this data into engine torque by means of the actuators.

The EPC circuit also monitors these components at start up and whilst driving and should it detect any malfunction, it will readily illuminate the EPC warning light . The EPC light is a bright yellow/amber instrument cluster light displaying the letters EPC. But it's just a 'Indicator Symbol light' that  informs the driver that an issue occurred in the torque system. Some faults within the EPC circuit will more than likely disable other functions on your vehicle that may even cause it to go into limp mode and not rev or perform very sluggishly.

EPC Warning Light

Since the EPC is a sub circuit of the ECU which supervisors several other systems on the vehicle, it is likely that other warning lights my also illuminate  on the instrument cluster. For example the Check Engine Light (CEL) may illuminate to indicate that the engine itself isn’t operating at normal efficiency. At the same time the stability and cruise control will be disabled and their respective lights may turn on as well.  

When this happens, you will need to have your car scanned for diagnostic trouble codes (DTC) or you could do it yourself if you have an appropriate scanner. Once the error codes are identified, it would be relatively easy to repair / replace the component responsible, and thereafter clear the fault codes. The illuminated lights should all turn off and the car should once again drive as per normal.

Is it safe to drive with the EPC light on?

Many people inquire  whether or not it safe to drive with the EPC light on? In my humble opinion, I would say,  Yes it is safe to drive with the EPC light on, because the EPC light is an abler light and not a red light. Red lights dictates that you shouldn't  drive the car at all, until the problem causing the red light to illuminate is repaired. Whereas an amber light is just an information sign. One can equate dashboard lights to road signs, for example if a red traffic light or a red stop sign with white-background  or other red and white regulatory sign is blatantly disobeyed, it will more likely than not result in harm or injury. Round red and triangular red road signs are warning signs and means danger. Also any sign with a white background signifies the sign is permanent  whereas a sign with a yellow background signifies that the sign is temporary and any square /diamond shaped orange/amber signs are used for roadway works information and guidance.

So return to the subject at hand, yellow/amber lights are therefore informative and temporary. However when the EPC light is on and the car goes into limp mode then its not safe to drive with the EPC light on, because you will be going dead slow and be an obstruction to other motorists. Limp mode is just a shortened form for limp home mode which is  an operating mode set by the vehicle's on-board  computer which is pre-programmed by the manufacturer. This program limits  your vehicle throttle in order to protect the engine or the car itself or its occupants from harm or injury and the car should only be driven to take it for  repairs.

As can be seen, the four signs on the right are red with the top two including white
whereas the four signs on the left are all yellow  which is informative and temporary. 

However the severity of the EPC problem can vary greatly and the vehicle may not be operable at all.  Common cause of  car’s EPC circuit malfunctioning are its sensors. Replacement normally solves the problem, however EPC faults can register intermittently to the point of frustration. In such cases it's very likely the wiring harness are intermittently faulty especially where the plugs connect to the sensors. If your engine suddenly shuts off while driving, you may want to look at the Engine speed sensor. The  crank shaft rotation sensor also commonly fail, when starting the car's engine while stationary. A tell tale sin is that the  the engine switches off after two second of idling. 

The brake light switch is yet another  EPC light trigger and is solved by replacement. This switch is a double pole double trow switch and isn't physically associated with the brake other than the same switch is used. On automatic vehicles brake switch failure locks the gear lever in Park and prevents  from selecting any other gear. The Mass air flow sensor is another common cause of EPC problems but in many cases it's not the MAF itself. It may be due to minor cracks in the rubber hoses that causes air to be sucked in, upsetting ECU calculations. The Throttle body and its angle sensors and drive motor is another is also another EPC problem child.

@volkswagenindia why am I getting EPC light again and again. Already 7 times repaired. Tired!! @Volkswagen pic.twitter.com/S1GzM6shNT

— विरल (@Viral_HS1) July 1, 2017

KNOCK SENSORS

KNOCK SENSORS

Gone are the days when you could fix your own car with simply logic. Today you require digital logic, a scan tool  and a tech savvy mechanic to make sense of the latest cars because they are all very precisely controlled by electronic circuits. The Engine Control Module is just one such circuit and largely depends on several of its sub-circuits and associated automotive control modules to achieve the precision needed to propel the latest engines using high octane fuel, and burn it stoichiometrically in order to deliver the performance expected from these modern cars. But this is easier said than done because these sub-circuits and associated control modules rely on a number of inputs sensors and actuators distributed all over the engine and the car in general, to successfully control of the crank synchronous path.

In order for the ignition sub-system to function optimally for example, it requires feedback information about what is presently happening in the engine so that it can take corrective action if needs be, in real time. Likewise the fuel mixture sub-circuit can only determine if the mixture is rich or lean from the feedback information, then take corrective action to increase or decrease the quantity of fuel based on the amount of oxygen present. Like wise the crankshaft timing sub-circuit depends on feedback information and maintain a constant torque. Yet all three these ECM sub-circuits works very closely in conjunction with one another and other sub-circuits to achieve optimal performance. 

Restated, the ECM is in control of the torque and torque reduction circuits, which just happens to annoy the arse-mousse out of Volkswagen, Audi, SEAT and Skoda owners. It is commonly referred to as the EPC -Electronic Power Control. Essentially EPC is limp mode's best friend and vehicle owners worst enemy.  ECM torque reduction is handled via the crank synchronous path, and involve the  ignition system sensors, the knock sensors, and fuel mixture both short trim and long trim. 

Input signals are needed for calculating precise ignition timing:

1) Engine Coolant Temperature Sensor (ECT)  

2) Engine Speed Sensor (RPM)  

3) Throttle Control Valve Sensor  

4) Camshaft Position Sensors

5) Knock Sensors  

6) Accelerator pedal Position sensors


By monitoring the Engine Coolant Temperature Sensor (ECT), the ECM varies the parameters of the engine as it heats up and maintains it when it has reached the correct operating temperature. 

By monitoring Engine Speed Sensor (RPM) the ECM can determine how many times the coils misfires per 1000 revolutions and how many times the injectors fail to deliver fuel. 

By monitoring the Throttle Control Valve Sensor the ECM can calculate the torque compared to how wide the throttle opens. 

By monitoring the Camshaft Position Sensors the ECM can better determine the exact time when the valves close and the exact point of ignition. 

By monitoring the  Knock sensors the ECM decides whether detonation is bad enough to take action, either  to retard / advance the engine or reduced the torque and consequently prevent engine damage. 

By monitoring the Accelerator Pedal Position sensors it can determine synchronicity between the position of the accelerator pedal when depressed and the throttle control valve and and discrepancy outside of its normal parameters will reduce the torque. 

KNOCK SENSORS

Knock sensors are very important to the overall engine torque because they detect combustion knocks in the individual cylinders. This is common when high octane fuel self ignites  which is generally known as knocking (detonation) or pinging (pre-ignition).
Knock sensors are piezo-electric components acts something like microphones do, but instead of picking up sound,  they detect vibrations in an engine which are needed by the ECM to correct the combustion process in the event of detonation or pinging.  This allows the ECM  to "retard" the engine so that it would work with different quality fuel. This implies that lower octane fuels are more prone to knock than higher octane fuels. It is therefore imperative to use the correct octane fuel prescribed for your vehicle since failure to do so can cause the EPC light to turn on and cause the vehicle to enter into limp mode.

TESTING KNOCK SENSORS

Four and six cylinder engines have 2 knock sensors each. Knock sensor 1 monitors the even bank of cylinders while Knock sensor 2 monitors  the odd bank of cylinders. W8 and W12 engine have 4 knock sensors each.  Knock sensor 1 monitors  cylinders  1 & 2, Knock sensor 2 monitors  cylinders 3 & 4, Knock sensor 3 monitors cylinder 5 & 6, and  Knock Sensor 4 monitors cylinder  7 & 8. Knock sensors are mounted directly on the crankcase and must be torqued. Failure to torque a knock sensor may cause it to malfunction and pickup engine vibrations as well as detonations.

The plug for Knock sensor (KS) 1 is normally green and it monitors cylinders  1 & 2, whereas the plug for Knock sensor (KS) 2 is normally grey and it monitors cylinders 3 & 4. Knock sensors are three pin devices with  Pin 1 = Signal, Pin 2 = Ground and Pin 3 = Shielding. Using a multimeter measure the resistance for "short circuit" between pins 1 and 2, then 1 and 3, then 2 and 3 at the Knock sensor connector. This measurements should always read infinity (open circuit).  If short circuit, replace knock sensor and make sure that it is correctly torqued to the crankcase.  Also check the wires for short circuit. If short circuit, replace. If a oscilloscope is available, connect it between pins 1 & 2 of the knock sensor. Tap the knock sensor lightly with a wrench, this should produce a fairly high frequency irregular sinusoidal waveform with a higher amplitude towards its middle. If there is no waveform coming out of the knock sensor its best to replace it because it will lead to a rise in fuel consumption and the engine management system may reverts to emergency knock control and reduce overall engine performance.