VW Bora TDI Preheating System Troubleshooting Guide

Having dealt with similar heating module issues on my VW Golf TDI 2001, I understand your preheating concerns. The symptoms you describe match what I experienced, constant glow plug light, check engine illuminated, and smoke issues. My car electronics diagnostic revealed a faulty connection between the control unit and the vehicle heater system. The cable connections had corroded over time, causing intermittent electrical fault signals. The workshop found the car preheater control unit itself was actually fine, they cleaned and reseated all connections, replaced one damaged wire, and recalibrated the system. Total repair cost was 95€ including diagnostic time. To provide more specific advice for your case, could you share: Current mileage, How long the problem has been occurring, Whether the issue happens more during cold starts, If you have access to diagnostic error codes These details would help determine if your Bora has the same underlying issue my Golf had or if something else might be causing these symptoms.

Latest service was 2 months ago at 94000km. After running diagnostics, error codes showed issues with the glow plug control module. The preheating problems started right after a particularly cold morning, getting worse over the past week. The engine preheat system seems most affected during cold starts, taking longer than usual to warm up. The electrical fault appears consistent with the symptoms you described on your Golf. Getting similar smoke issues especially when accelerating. The vehicle heater itself works fine for cabin heating, which makes me think the control unit might indeed be the culprit rather than the entire heating module system. Will try checking the connections first before replacing parts. Wondering if cleaning the connections alone might solve it, given how similar these symptoms are to what you experienced. The quoted replacement cost for a new control unit is 450€, so exploring cheaper fixes first seems sensible.

Thanks for those additional details. Your symptoms do match even closer to what I experienced with my Golf TDI now that you mention the cold start trigger and the working cabin heat. In my case, checking the connections revealed significant corrosion on the control unit pins, likely from winter moisture build-up. The ignition system diagnostic showed intermittent voltage drops, which explained the constant preheating lamp and smoke issues. A thorough cleaning of the control unit connections with electrical contact cleaner and ensuring proper grounding solved about 80% of the issues immediately. The workshop then needed to recalibrate the engine preheat timing through the car electronics system to fully resolve the remaining symptoms. Given the age of these TDI models, the car preheater control connections often develop these issues around 90-100k km. Starting with connection cleaning and diagnostics makes sense before spending 450€ on a new unit. Would definitely recommend having a professional workshop: Clean all control unit connections, Check ground points, Verify glow plug resistance values, Run a full system diagnostic afterward The complete service should cost significantly less than a new unit, probably around 120-150€ including diagnostics.

Thanks for the detailed feedback. After checking at the workshop today, you were absolutely right about the connections. The electrical fault turned out to be mainly due to corroded pins on the control unit, exactly as you described. The mechanic cleaned all the car preheater connections and found one loose ground wire that was causing additional issues with the vehicle heater system. Total repair cost came to 135€, including a full diagnostic scan and recalibration of the engine preheat timing. The smoke during acceleration has completely cleared up, and the preheating lamp now functions normally. The heating module responds much quicker during cold starts too. Saved over 300€ by fixing the connections instead of replacing the entire control unit. Really glad I checked the forum before buying new parts. Will definitely keep an eye on those connections during future services, especially before winter when the car electronics need to be in top shape.