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The EPC light is for the electronic throttle body. It stands for Electronic Power Control. This is the drive by wire throttle system used in Audi and VW gasoline vehicles.
Here is how the system works. There are two sensors inside the throttle body. They mirror eachother. For exmaple, one voltage will go up while the throttle plate opens and the other voltage will down down. The two sensors sweep in opposite directions for plausibility testing (i.e. one goes from 0.5 V up to 4.5 V while the other goes from 4.5 V down to 0.5 V). If the voltage of the two sensors is added together, it should equal the reference voltage into the sensors. The Major inputs to the calculation for the EPC system are:
- Throttle Position Sensor G79 - Sender 2 for Accelerator Pedal Position G185 - Throttle Valve Control Module J338 - Angle Sensor 1 for Throttle Drive G187 - Angle Sensor 2 for Throttle Drive G188 - Brake Light Switch F - Mass Air Flow (MAF) Sensor G70
Any fault codes or situations that can affect how the throttle body is controlled or will respond can cause the EPC light to illuminate.
I hope this helps!!