Continued from EPC DEMYSTIFIED CONTINUED 1.
... I only became aware of this when my
EPC light went on due to the knock sensor.
See picture blog. More...
PART 3
BREAKING THE CODE
What needs to be mentioned as a basis of understanding, is that OBD (on-Board Diagnostics) was introduced in the 70's along with CDI (capacitive discharge ignition systems) as DIY kits. Few cars had fuel injectors, points and coils were fast being taken over by electronic modules. During this time some standards were introduced but they were not very well defined and as such manufacturers developed their own and applied their specific systems and developed their own code descriptions which later became known as OBD1. This was considered undesirable and counterproductive since none franchised service, and general mechanical repair centers had to purchase different scan tools, interface cables and connectors, skills and manuals for each make and model of car they specialized in. This resulted in vehicle diagnostics becoming unwieldy expensive. In February of 1986, Robert Bosch founder of Bosch, introduced the CAN (Controller Area Network) serial bus system to the Society of Automotive Engineers (SAE) in motor town of Detroit.
This influenced the Society of Automotive Engineers (SAE) who subsequently drafted a list of standards and practices that aught to be implemented by all automobile manufacturers and recommended them to the Environmental Protection Agency (EPA). The EPA weighed-up these standards and recommendations, acknowledged their benefits, and adopted them. The standards criteria included a precisely defined diagnostic connector for each auto manufacturer, a standard scan tool and a common electrical communications protocol and a common data format, and the ability to monitor other
vehicle parameters. Lastly that the standard scan tool should interface with vehicles of all manufacturer. It also included mandatory definitions and descriptions for certain emission control system defects which was labeled the ‘
P0’ Codes. Manufacturers were allowed to generate and use their own ‘manufacturer specific code descriptions’ known as ‘
P1’ Codes. This collaboration of standards became known as
OBDII, (OBD2) and was adopted for implementation by January of 1996. Two types of scanner codes, namely manufacturers codes like VAG codes and SEA Codes are now the standard practice.
OBD-II
As mentioned above, Powertrain Control Module (PCM) error codes are assigned the prefix P and pertain to the, Engine management, Transmission management, Fuel Pump and Gasoline Management, Automatic Transmission – Hydraulic Control, Emission control system, evaporative emission purge control (HVAC), Auxiliary module management and other some 0n-board Hybrid application. For example P1340 suggests that the Powertrain triggered a DTC and describes it as an "Crankshaft-/Camshaft Position Sensor Signals Out of Sequence"
From the above example it would thus be easy to interpret the DTC below relating to
EPC (Electronic Power Control)
DTC (VAG) DTC (SAE) Society of Automotive Engineers
16504
P0120
Throttle Position Sensor A - Circuit Malfunction
16505
P0121
Throttle Position Sensor A - Circuit - Performance Problem - Out of Range
16506
P0122
Throttle Position Sensor A Circuit - Low Voltage Input
16507
P0123
Throttle Position Sensor A Circuit - High Voltage Input
16894
P0510
Throttle Position Sensor - Closed Switch- idle micro-switches -F60 malfunctioning
17951
P1543
Throttle Actuation Potentiometer - Signal too Low
17952
P1544
Throttle Actuation Potentiometer - Signal too High
17913
P1505
Throttle idle micro-switches -F60 not/short-circuit opens
17914
P1506
Throttle idle micro-switches - Switch Does Not Open/Short to Ground
17988
P1580
Throttle Actuator (B1) Fault - May be caused by low battery if found with 16487 (P0103)
18038
P1630
Accelerator Pedal Position -G79 signal too small (low)
18039
P1631
Accelerator Pedal Position -G79 signal too largely (high)
18040
P1632
Accelerator Pedal Position -G79 supply voltage malfunction
18041
P1633
Accelerator Pedal Position -G185 signal too small
18042
P1634
Accelerator Pedal Position -G185 signal too largely
18047
P1639
Accelerator Pedal Position 1+2 Range/Performance -G79 and -G185 implausible signal
18048
P1640
Internal Controller Module defective (EEPROM) Error
EPC Circuit.
The
EPC circuit consists of a number of disparate components that control and supervise, regulate and determine the throttle valve position at all times. They include;
1) the accelerator pedal position sender (TP sensor G69)
2) the accelerator pedal position sender -2, (G185)
3) Black 6-pin plug with 6-pin with Gold plated contacts
NB! The above three components are part of the accelerator pedal.
4) the throttle valve control module (unit),
5) the K132
EPC fault lamp, (electronic throttle control fault indicator)
6) the engine control module (unit).
Firstly we going to do a test on components 1, 2 and 3 above. To do this test, you need a Fluke multimeter or similar for a voltage and continuity / resistance test. Unplug the 6-pin plug from the accelerator pedal and switch on the ignition. Connect the multimeter and check for a 4.5 volt reading between;-
pin 1 and ground, then between pin 1 and pin 5
Pin 2 and ground, then between pin 2 and 3.
If tests prove to be "OK", switch ignition off.
Do additional checks for short circuits between one another and ground and if this checks "OK",
Locate the ECU, normally inside cowl. Disconnect the ECU from its socket, identify pins 34 & 34, 35 & 36, and 72 & 73 on the socket. Disconnect the 6-pin plug from the accelerator pedal once again and check for continuity between this plug and the ECU socket. There should be continuity between pins:-
1 of the 6-pin plug and pin 72 of the ECU socket.
2 of the 6-pin plug and pin 73 of the ECU socket.
3 of the 6-pin plug and pin 36 of the ECU socket.
4 of the 6-pin plug and pin 35 of the ECU socket.
5 of the 6-pin plug and pin 33 of the ECU socket.
6 of the 6-pin plug and pin 34 of the ECU socket.
Any resistance above 1.5ohms should be investigated for corrosion. This often causes the engine to surge (idle unevenly or rather breaths) However, if this test proves "OK" and no wiring malfunction is detected, replace G69 and G185 (single unit) on the accelerator pedal. NB! these components are non adjustable and needs to be replaced as a whole.
When the ignition is turned on, the ECU checks all
EPC components necessary for the proper functioning of the Electronic Power Control. If a malfunction is detected in the
EPC (Electronic Power Control) system whilst the engine is running, the ECM will simultaneously activate the
EPC (Electronic Power Control) warning light and make an entry of this malfunction in the ECU (electronic Control unit) DTC (Diagnostic Trouble Codes non-volatile memory. By a process of eliminate the
EPC fault can be fixed.
The list below categorises VW and Audi manufacturer predetermined data groups which varies depending on the vehicle, year, engine, engine code and management system on board.
Group Number / Group Category
1–9
General engine activity data
10–19
Ignition data
20–29
Knock control data
30–39
02 sensor control system data
40–49
Three-way CAT data
50–59
Engine speed control data
60–69
Throttle drive data
70–79
Emissions reduction data
80–89
Special function data
90–97
Power increase data
98–100
Compatibility data
101–109 Fuel Ignition data
110–119 Boost pressure control data
120–129 Control unit communication data
130–150 Special info data
Based on the data from the above table
EPC problems are associated with group 60-69. However, on Expert Systems Diagnostics Group 60, holds the
EPC Adaptation data, group 61 holds
EPC-system 1 data and group 62 holds the
EPC system 2 data. Group 66 holds the speed-o-cruise data.
NB! If you found this information useful, please link to this page.
