VW Scirocco ECU Failure: Symptoms and Repair Guide

I faced a similar issue with my VW Golf GTI 2014 last summer, and having some experience with VW electronics, I understand your concern about ECU problems. The symptoms matched what you describe, reduced engine performance and error codes. Initially thought it was the ECU, but after diagnostic testing, the workshop found the main relay was defective. The faulty relay was causing intermittent power supply issues to the engine control system, simulating ECU failure symptoms. The repair involved: Complete system diagnostics, Testing the power supply to the ECU, Main relay replacement, ECU system reset, Final performance testing Total cost was 120€ including parts and labor. Engine performance returned to normal immediately after the fix. Before jumping to ECU conclusions, could you share: What specific error codes appeared? Does the problem occur more during cold starts? Are there any other electrical issues like flickering dashboard lights? Have you noticed problems with starting the car? This information would help determine if your issue matches the relay problem or points to actual ECU repair needs.

Just had my 20000km service last month and all was fine until this started. After reading your reply about the relay, I checked and got these error codes: P0603 and P0606. The car mostly struggles during morning starts when cold, but no issues with dashboard lights or starting. The engine performance drops are quite unusual during drives, which matches what you described about intermittent power supply. This insight about the relay is really valuable, definitely worth checking before replacing the entire engine control unit. Will ask the workshop to specifically test the power supply and relay system during car diagnostics.

The error codes you mentioned (P0603 and P0606) align perfectly with what I experienced before discovering my relay issue. These codes typically point to engine control module processor or memory problems, but in my case, and possibly yours, the root cause was the power supply inconsistency. Since your symptoms match mine almost exactly, especially the cold start problems and unusual performance drops, I strongly suggest having the relay circuit tested first. A faulty relay can mimic ECU failure by causing intermittent power disruptions to the engine control systems. One quick test my technician performed was monitoring voltage fluctuations at the ECU while the engine was running. This helped identify the relay as the culprit rather than internal ECU failure. The automotive electronics specialist confirmed that VW models from this era sometimes develop relay issues around this mileage point. After the relay replacement and system reset, my engine performance returned to normal, and the error codes never came back. The repair cost was far less than a new ECU would have been. Make sure your workshop includes relay testing in their car diagnostics process, it could save you significant repair costs. Let us know what your technician finds. If it turns out to be the relay, you should see immediate improvement after replacement.

Thanks for all the feedback! I really appreciate getting your insights about the relay issue. I made an appointment with my regular workshop for tomorrow morning and specifically mentioned the relay testing you suggested. I sent them the error codes and symptoms beforehand, plus mentioned the voltage monitoring test you described. The coincidence with the mileage point and VW models makes a lot of sense too. Very hopeful this might be the solution since vehicle electronics repairs involving the complete ECU would be way more expensive. Will update here after the car diagnostics session. If the system reset and relay replacement fix the engine control problems like in your case, this thread might help other VW owners facing similar issues. Again, grateful for helping me potentially avoid an unnecessary ECU replacement. The detailed explanation about testing the power supply to isolate the actual problem was exactly what I needed to discuss with my mechanic.