VW Golf TDI Power Loss: ECU Failure Warning Signs

I dealt with very similar automotive electronics issues on my 2000 VW Passat TDI. Having some experience with car diagnostics, I first thought it was the ECU too, but it turned out to be much simpler. The symptoms were identical, power loss, rough running, and multiple error codes from the control system. My mechanic started with basic troubleshooting of the engine control circuits and discovered the main relay was defective. When these fail, they can cause confusing symptoms that mimic ECU problems. The repair was straightforward, replacing the main relay fixed all issues, and the total cost was 120€ including parts and labor. The car has been running perfectly since then. Before suggesting more specific solutions, could you share: Does the problem occur when the engine is cold or warm? Are there any other electrical issues like flickering lights? What specific error codes did the diagnostics show? Have you noticed any issues with starting the car? This information would help determine if your symptoms match what I experienced with the relay issue versus a more serious ECU problem.

Just had my last service at 142000km and the mechanic did a thorough check of all engine control systems. The engine problems start after about 15 minutes of driving when the engine is warm. No issues with the lights or other electrical systems. The error codes point to multiple sensor failures, P0401, P0340, and P1403. The car starts normally, but the engine performance drops significantly once warmed up. The erratic behavior and timing of the issues make me think its more than just the relay. I will get the wiring harness checked first since damaged wiring could explain the multiple sensor readings. My concern is that water damage might have affected the ECU itself, as there was some dampness in the engine bay after heavy rain last week.

Thanks for those additional details about your VW Golf. My Passat had very similar symptoms after rain exposure, and checking the wiring harness was exactly my next step too. In my case, water had indeed seeped into the engine bay and corroded several connector pins in the wiring harness near the ECU. The multiple error codes and sensor failures were caused by poor electrical connections rather than actual sensor or ECU problems. A thorough inspection of the engine control system revealed several compromised spots in the wiring insulation. The repair involved: Cleaning and resealing all connectors, Replacing damaged sections of the wiring harness, Applying dielectric grease to prevent future corrosion, Performing a system reset after repairs Total repair costs came to 350€, which was much cheaper than replacing the ECU. The car diagnostics afterward showed all sensors working normally, and engine performance returned to normal. Since your symptoms started after rain exposure, I suggest having your mechanic specifically check for water intrusion points around the ECU and wiring harness. These VW models from that era are known to develop seal deterioration that allows moisture into critical areas.

Your car symptoms match a lot of experiences shared here. After getting this input and doing more research, I will have my mechanic focus on checking the wiring harness and water seals first, since the timing with the recent rain seems more than coincidental. The multiple error codes showing on my car diagnostics appear very similar to what others experienced with water damage issues. Replacing the complete ECU would cost over 1000€, so starting with the wiring inspection makes more sense financially. The computer module might be fine, and the engine performance issues could be from corroded connections. Will schedule an appointment to have them inspect all the electrical connections and seals around the engine control system. If they find water damage, I expect repair costs around 350-400€ based on the feedback here. That seems reasonable compared to a full ECU replacement. Thanks for helping narrow down the likely cause. Will update once the vehicle electronics inspection is complete and we know if water intrusion was indeed the culprit.