The EPC light has come on twice now, but hasn’t stayed li...

Hello, my name is \*\*\*\*\* \*\*\*\*\* I will be helping you with your question today. I've been working on Audis for over 30 years now, so I should be able to help you through this. Please understand that some of my suggestions may require special diagnostic tools and equipment that many home mechanics may not have, but are often required. So, my first question is whether you're planning on performing your own repairs, or are you wanting to be armed with information before bringing it into your mechanic? **Also, the site automatically prompts for a phone call. It's very rare that I'm available by phone, so let's hold off on that for now. If needed after we exchange some information, I will do my best to take the time for the call.** Couple of other questions 1) you've mention that you've scheduled a diagnostic scan, is it with a good Audi independent shop of more of a general shop? 2) would you like a bit more information about what the EPC system is and how it functions?

Hi there, Jason! I want to be armed with proper information to give a mechanic.1)I scheduled the scan with yourmechanic.com, hoping they could provide codes I'd need to provide.2) I have a basic understanding of the EPC system.Thank you

Ok, I'd be a bit dubious about the yourmechanic.com house call, but being honest, I don't know what equipment they're using to scan. To get some good solid diagnostic data, a scan using VCDS or other Audi specific scan tool is needed here. However, to answer your original question, yes, the engine computer does store fault codes until repaired or cleared. Bit of an EPC overview (some of the specific designations vary among models) 1. **EPC** stands for Electronic Power Control. This is the drive by wire throttle system used in Audi Lamborghini and VW gasoline models starting around the 2001 m.y. 2. How the system works: A. 2 position sensors located on the accelerator pedal (Throttle Position (TP) Sensor G79 and Sender 2 for Accelerator Pedal Position G185) transmit driver demand (intent) to the Engine Control Module (ECM). i. The G185 signal is always 1/2 of the G79 signal for plausibility testing. B. The ECM interprets the signals from the G79 and G185 sensors along with signals from other systems (engine, ABS, AC, transmission) to determine the output power sent to the Throttle Valve Control Module J338. C. The Throttle Valve Control Module J338 receives the power from the ECM and moves accordingly. There are 2 position sensors on the J338 module (Angle Sensor 1 for Throttle Drive G187 and Angle Sensor 2 for Throttle Drive G188) that provide feedback to the ECM on the current position of the throttle plate. i. 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. 3. Major inputs to the calculation for the **EPC** system are: - Throttle Position (TP) 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 4. Any fault codes or situations that can affect how the throttle body is controlled or will respond can cause the **EPC** light to illuminate. 5. In a Key On Engine Off (KOEO) situation, the throttle plate should respond according to the accelerator pedal. (i.e. if the accelerator pedal is depressed 1/2 way, the throttle plate should open 1/2 way.) 6. If the engine is running, the ECM calculates the opening of the throttle plate based on multiple inputs (see step 2B). So, hopefully their equipment will pick up the correct fault information. I'm happy to audit it as necessary when you have it done

The typical reasons for that light in these particular cars: 1) throttle body electronic failure 2) throttle pedal. Both relatively quick and easy to replace.

They won't be here to scan it until Friday. Would you recommend taking it somewhere instead? The EPC light isn't on currently.Thank you very much for the information

For issues like this, I tend to recommend a place familiar with Euro/Audi, and this is a good locator: [https://www.fourringsrepair.com/](https://www.fourringsrepair.com/)

Ah okay. I appreciate it.

Sure thing