Audi A3 Diesel Power Loss: ECU or Engine Trouble?

I had nearly identical symptoms on my 2016 Audi A4 2.0 TDI. The engine performance dropped significantly and engine control warnings appeared. After proper diagnostics, it turned out the main relay was failing, causing intermittent power supply issues to the engine control module. The repair required replacing the main relay and performing a complete system reset of the vehicle electronics. This wasnt a major repair in terms of complexity, but leaving it unfixed could have led to more serious issues with the engine control systems. The symptoms you describe, power loss combined with persistent check engine warnings, strongly suggest an electrical supply problem rather than a mechanical issue. When the main relay fails, it affects multiple automotive electronics systems, particularly those controlling engine performance. Since this involves critical engine control components, I recommend having it checked at a shop with proper diagnostic equipment for vehicle electronics. A failing main relay can sometimes be misdiagnosed as ECU failure, so proper testing is essential before replacing more expensive components.

Thanks for sharing your experience with the main relay issue. I went through something very similar with my Audi A3 last year. Would you mind sharing how much the repair ended up costing? Really curious since car diagnostics and labor costs vary quite a bit. Also, have you had any recurring engine performance problems since getting it fixed? My mechanic mentioned these electrical issues can sometimes indicate other underlying problems with the engine control systems, so Im interested in knowing if everything has been running smoothly for you.

After getting the main relay replaced, my engine control systems have worked flawlessly. The repair cost was 120 Euro including diagnostics and labor, which was quite reasonable considering the improvement in engine performance. The vehicle electronics have been completely stable since the fix, no check engine lights, no power issues, and the computer module is functioning as it should. The mechanic performed thorough car diagnostics to ensure there were no other underlying problems affecting the engine control unit. Its been over a year now, and Im happy to report zero recurring issues. The initial symptoms completely disappeared after the main relay replacement. This confirms it was indeed an electrical supply problem rather than a more serious engine control system fault.

I followed through with getting my A3 checked out and the diagnosis matched exactly what you described. Took it to a specialized shop with proper car diagnostics equipment. They found the main relay was indeed the culprit causing the ECU problems. The repair cost me 140 Euro total, slightly more than yours but still reasonable. The engine control system is now working perfectly again. The power delivery is back to normal and all warning lights have cleared up. The computer module readings are all within normal range. It was a relief that it wasnt a major engine control unit failure like I initially feared. The shop did a complete system scan after the repair to verify no other components were affected. Been driving for about two weeks now without any issues, no more power loss or error codes. Really glad I asked here first instead of potentially overpaying for unnecessary repairs. Getting accurate car diagnostics from a shop that understands these control systems made all the difference.