Electronics have taken the motor industry by storm, so-much-so, that electronic black boxes and discrete components have come to replace several mechanical systems. As a result, provided us with increased safety features, tighter and better engine control, additional creature comforts, convenience and so much more. Virtually every system in the modern day car is digitally controlled by a some Electronic control Unit (ECU) or a bank of dedicated onboard computers distributed throughout the car, all of them networked to a Central Bus System. There are numerous bus systems used in electronics but CAN bus developed by Robert Bosch in 1986, has quickly gained acceptance into the automotive and aerospace industries. With the continued development of more complex ECU applications, much larger quantities of data needed to be processed, scores of more signals needed to be measured, and a growing number of other parameters needed to be optimized.
CAN bus was the answer to surmount these problems though it is essentially a serial bus protocol used to inter connect individual sub systems and sensors as an alternative to conventional multi-wire looms. In a nutshell, cars have gone electronic processors, is firmware based, software driven and data analysed, artificially semi-intelligent and electronically complex. All of a sudden automotive mechanics needed to learn loads of new words like microprocessor, microcontroller, quantitative analysis, electronic engine-management systems, potentiometer, sensors, signal processing, frequency response, memory-mapped let alone how their individual functions. To add insult to injury, abbreviations like Controller Area Network (CAN), CPU (central processing Unit), RAM (Random Access Memory), EPROM (Electronically Programmed Read Only Memory), LAN (Local Area Network), ADC (Analogue to Digital Converter), distributorless ignition system (DIS), etc, just flooded the motor vehicle repair market.
Talking about abbreviations, EPC, is the official abbreviation for Electronic Power Control when referring to the Drive-by-Wire Torque circuit though it also stands for Electronic Pressure Control when referring to the Automatic Transmission. When the Torque control EPC circuit fails for whatsoever reason, the EPC Warning Light (K132) located in the instrument cluster lights up, which then could cause the car to enter into "limp mode", depending on the severity of the problem. Limp mode is a protective state that the car's ECU enters into when it recognizes that there is a problem with it's logic program. For example, when an expected signal value originating from a sensor varies significantly from the predetermined program specification, the ECU then enters into a secondary/ emergency progromme in order to protect the engine / transmission from damage. The ECU is constantly expecting a regular stream of signal values from various sensors, like for example the Throttle Position Sensor, or the Mass air Flow Sensor, or the Engine Speed Sensor, or the temperature sensor, etc. As long as these signals stay within specified parameters for certain operating conditions, the ECU performs faultlessly at controlling the engine.
Due to the rapid expansion of electronics in motor vehicles, automotive mechanics in general were over whelmed by the introduction of this new evolution in technology and as a consequence didn't stay abreast of automotive electronics, thus now seem to have great difficulty in solving electronic problems on client's cars. Replacing parts indiscriminately with the hope that they get lucky and that the actual faulty component is among the suspected parts that were replaced. Many, many, many VW, Audi, Skoda, and Seat owners can testify to this, since most have first hand experience of taking their vehicles into the service agent, only to get the car back after having to foot an enormous bill for replacement parts that probably weren't faulty in the first place, only to discover later that the problem the car was taked-in for, still persists. EPC problems essentially have most VW "mechaicians" by the short and curlys. But an EPC problem is not that difficult to eliminate if checked systematically instead of trying to trace it by replacing components by substitution.
DESCRIPTION OF HOW THE EPC WORKSWhen the ignition is initially switched on, the Motronic Engine Control Module (ECM) performs a quick self diagnosis of all components that are important for the correct functioning of the Electronic Power Control. If all components pass the diagnostic test the EPC light goes out. However, should the Electronic Power Control (EPC) Warning Light not light-up when ignition is switched on, or if a malfunction is detected in Electronic Power Control system whilst the engine is idling, the Motronic Engine Control Module (ECM) will turn on the Electronic Power Control (EPC) Warning Light, sort of constantly. When this happens, a DTC entry is made in the Motronic Engine Control Module, then its time to scan for Diagnostic Trouble Codes with a scan tool.