Passat Hybrid Warning Light + Rough Idle Issues Solved

Having dealt with a similar issue on my 2015 VW Passat GTE Hybrid, I can share my experience. Not a pro mechanic, but I do have some basic car repair knowledge. The symptoms you describe match what I encountered. My check engine light also kept coming on, and the car felt sluggish with poor fuel economy. Initially thought it was the knock sensor, but after inspection at the workshop, they found a loose wiring connection to the engine control module. The auto repair involved checking the entire wiring harness and they discovered a damaged plug connection that was causing intermittent signal issues. The ignition timing was affected, leading to rough idling. Total cost was 95€ for diagnosis and repair of the cable connection. Before suggesting more specific solutions, could you share: Current mileage on your Passat, Whether you notice any specific driving conditions when the problems occur, If you have access to an OBD scanner to read the error codes, Any recent work done on the car Getting these details would help determine if your issue is similar to what I experienced or if its something else entirely.

Last service was done at 65000km, currently at 68232km. The OBD scan shows error code P0325, pointing to the knock sensor circuit. The rough idling seems worse during cold starts and the poor performance is most noticeable during acceleration. The dealer service department quoted 450€ for diagnosis and potential sensor replacement. Sounds steep compared to your wiring fix. Maybe worth checking the wiring connections first since you had success with that approach. Did your mechanic mention any other symptoms they typically look for to confirm knock sensor issues versus wiring problems? Would help to know what specific tests they ran before starting repairs.

Thanks for those details. My repair situation started similarly with the P0325 code, but after dealing with it, I learned there's more to check before jumping to sensor replacement. My workshop first did a visual inspection of the knock sensor wiring harness, which is a lot cheaper than immediately replacing parts. Their diagnostic approach included testing the sensor resistance and checking signal voltage, both tests that good auto repair shops should do before suggesting replacements. The engine knock symptoms in your Passat match my experience exactly, especially the cold start issues. My mechanic explained that while bad wiring and faulty knock sensors can show identical symptoms, there's a simple test they do: they check if the sensor signal changes when lightly tapping near the sensor mounting point. In my case, the signal stayed flat, pointing to the wiring issue. Since your mileage is close to where I had my problems (I was at about 67000km), and the symptoms are identical, I would strongly suggest asking your workshop to: 1. Check the wiring connections first 2. Test the knock sensor signal response 3. Verify the sensor ground connection The 450€ quote seems high if they havent done these basic checks. My complete diagnosis including the wiring repair was significantly less. If you decide to go ahead with their service, make sure they confirm its actually the sensor thats causing your car problems and not just the wiring.

Appreciate the detailed response regarding the diagnostic steps. Helpful to know about that tap test for checking knock sensor response, definitely something I'll ask the workshop about. Those three check points you listed make a lot of sense, especially since our cars had such similar mileages when the issues started. I called another repair shop that quoted 180€ for full diagnosis including the wiring inspection and sensor testing. Quite a difference from the dealer price. Booked an appointment with them for next week to check the wiring first, since the malfunction indicator and poor performance symptoms match your experience so closely. Will update once they identify whether its just a wiring issue or if I actually need the knock sensor replaced. Really hoping its the simpler fix like in your case. Thanks for helping me avoid potentially unnecessary parts replacement and saving some money in the process.