VW Fox Diesel ECU Failure Causing Power Loss Issues

As someone with moderate experience working on VWs, I encountered a similar issue with my 2006 VW Polo diesel. The symptoms matched yours exactly, reduced power and stored fault codes in the engine control system. Initially, I suspected a complete computer module failure, but after having car diagnostics performed, the workshop discovered it was actually just a faulty main relay. This component affects the entire engine control system and can mimic symptoms of ECU failure. The repair process involved: 1. Full system diagnostic scan 2. Testing the power supply to the engine control unit 3. Identifying the faulty relay 4. Replacing the component 5. Performing a system reset Total cost was 120€ including parts and labor. The fix restored full engine performance and cleared all fault codes. Before suggesting specific solutions, it would help to know: What specific fault codes are stored? Does the issue occur when the engine is cold or warm? Have you noticed any other electrical issues? Are there any other warning lights on the dashboard? This could help determine if you are dealing with the same root cause or if your engine control system has a different issue.

Last service was performed 2 months ago at 22943km. The fault codes are P0605 and P0700, both pointing toward the ECU problems you mentioned. The issues appear consistently regardless of engine temperature. The check engine light stays on continuously. When running car diagnostics, the workshop tested voltage outputs and found unstable readings from the computer module. They suggested either a full ECU replacement or repair of the existing unit. The engine control performance has gotten worse over the past week. Getting a quote for 950€ for a new unit seems steep. Wondering if rebuilding the control system might be a more cost-effective solution given the age and mileage of the vehicle. Has anyone tried repairing rather than replacing their engine control unit with success?

Thanks for providing those specific fault codes, they do point to internal ECU problems, but my experience with my VW Polo suggests it might not require a complete replacement like I initially thought. After dealing with similar control system issues, I first tried the ECU repair route. The repair specialist found corroded connections on the circuit board inside the engine control unit. The total repair cost was 380€, which included cleaning, resoldering connections, and recalibrating the unit. The unstable voltage readings you mentioned were exactly what my car diagnostics showed. However, before committing to any expensive repairs, have your workshop check: 1. The ground connections around the ECU 2. The wiring harness for any signs of water damage 3. The ECU housing seal integrity These checks helped identify the root cause in my case. The vehicle electronics were affected by moisture infiltration through a deteriorated seal, leading to internal corrosion. The repair has held up perfectly for 2 years now, making it a much better value than full replacement. If your ECU shows similar internal issues, I would recommend trying the repair option first.

Thank you for all the detailed information and suggestions. After considering the feedback about ECU repair versus replacement, I decided to have a specialist inspect the computer module before committing to the 950€ replacement option. The fault codes P0605 and P0700 combined with the unstable voltage readings definitely indicate control system issues, but getting a second opinion on repair possibilities seems wise. I will have them check the ground connections, wiring harness, and ECU seals as suggested. I contacted a vehicle electronics repair shop that specializes in engine control unit repairs. They quoted 400€ for diagnostic testing, repair, and recalibration if the issue is repairable. This seems more reasonable than full replacement, especially considering the age of my Fox. Will schedule the ECU inspection next week and have them perform a complete system reset after repairs. Hoping this resolves the engine performance issues without needing the more expensive replacement option. Will update once I know more about the actual condition of the control unit.