A8 Diesel Power Loss: Bad Fuel Filter Heater Alert

Had a similar issue with my 2010 A6 diesel. As someone who does basic maintenance but leaves complex repairs to professionals, these symptoms rang a bell. My car showed the same problems, power loss during acceleration, rough idle and poor fuel economy. After a thorough check, the workshop found a faulty cable connection to the fuel filter heater. The repair involved replacing the wiring harness and connectors. Total cost was 95 Euro for parts and labor. The fuel filter heater is crucial for cold starts in diesel engines, preventing fuel from gelling. A bad connection can definitely cause the symptoms you describe. Before making specific recommendations, could you share: Current mileage, When was the last fuel filter change, Any other warning lights on the dash, Does the rough idle happen more during cold starts This would help determine if your issue is identical to what I experienced or if there might be other factors at play.

Thanks for the follow-up. My current mileage is 16588 KM and I had the last service done just two months ago where they checked the fuel lines and performed routine maintenance. The rough idle is definitely worse during cold starts and gets slightly better as the engine warms up. The fuel efficiency has dropped from my usual average by about 20%. No other warning lights are present besides the initial fault code. Your experience with the wiring harness is interesting since my mechanic initially suggested checking the fuel filter itself rather than the connections. Will ask them to specifically inspect the electrical connections to the heater unit when I bring it in. Would you recommend any specific checks I should have them perform while diagnosing the fuel system issues?

Based on my experience with the same issue, your symptoms strongly align with what I encountered, especially the cold start behavior and fuel efficiency drop. The initial fuel filter inspection your mechanic suggested is logical, but given the similarities to my case, the wiring should definitely be checked first. The fuel filter heater connection problems often mimic symptoms of a clogged filter. Since you had recent maintenance, I would recommend having them: 1. Check the wiring harness connections to the fuel filter heater first 2. Test the fuel filter heater function during cold start 3. Verify fuel system pressure across different operating temperatures 4. Inspect the fuel lines for any potential restrictions In my case, the fuel efficiency improved immediately after fixing the wiring issue. The rough cold starts completely disappeared, and normal engine response was restored. The repair was straightforward once properly diagnosed. Given your recent service and relatively low mileage, I doubt you are dealing with a clogged fuel filter. The electrical connection to the heater is likely the root cause, just as it was in my situation.

Thanks everyone for the detailed responses. This really helps narrow down the potential issues. After considering the feedback, I will have my mechanic focus on the electrical connections to the fuel filter heater first, since my symptoms match so closely with the wiring harness problem described. The fact that the rough idle improves as the engine warms up seems to support this theory. I have scheduled an appointment for next week and specifically requested they: Check all wiring connections to the fuel filter heater, Test the heater function during a cold start, Verify fuel system pressure, Inspect the complete fuel line system Given my recent maintenance and the similarity of symptoms, I am hopeful this will turn out to be a relatively straightforward electrical issue rather than a more complex fuel system problem. Will update once I have the diagnosis and repair completed. Thanks again for helping me better understand the likely cause of my diesel engine power loss and rough idle issues. This information will definitely help me have a more informed discussion with my mechanic.