Q5 Diesel Cold Start: Bad Glow Plugs Warning Signs

I had a very similar issue with my 2016 Audi Q3 diesel engine last winter. As someone who does basic maintenance but leaves complex repairs to professionals, I can share my experience. The symptoms matched yours exactly, problematic cold starts, engine light on, and rough running when cold. Initially thought it might be fuel-related, but the diagnostic showed a faulty glow plug in cylinder 2. The workshop found that moisture had damaged the plug and its wiring. The total repair cost was 440 Euro, which included: New glow plug replacement, Diagnostic test, Labor costs, System reset After the repair, the engine misfire issues disappeared completely, and cold starts became smooth again. The diesel engine now runs perfectly, with much better fuel efficiency than when the glow plug was failing. To provide more specific advice about your case, could you share: Current mileage on your Q5, How long has the engine light been on, Whether you notice any smoke during cold starts, If you have already had any diagnostic tests done These details would help determine if your situation is similar and if you might need additional checks beyond the glow plugs.

Thanks for sharing your experience. Just had my service at 14569 KM a week ago and this issue started right after. The check engine light started flashing yesterday morning. My diesel car now produces white smoke during cold starts, which I did not mention earlier. Did get a basic diagnostic scan yesterday from a local shop, they found error code P0381 which seems related to the glow plug system. Given the timing right after the service, I wonder if something was disturbed during maintenance work that could have affected the glow plug circuit.

Thanks for those additional details. The timing after your service is interesting, as I had a somewhat similar experience with my Q3 where issues emerged shortly after maintenance. The white smoke during cold start combined with error code P0381 strongly suggests a glow plug control module problem rather than just a faulty glow plug. In my case, the initial diagnosis of just a bad glow plug turned out to be incomplete, the wiring harness connecting to the glow plug control unit had been accidentally disturbed during routine maintenance. The complete fix for my diesel engine involved: Inspecting the entire glow plug wiring system, Replacing a damaged wire connector, Testing the glow plug control module, Performing a system reset Total cost ended up at 580 Euro rather than just the 440 Euro for the simple glow plug replacement I mentioned before. Given your car just had service, I recommend having the shop check if any connections were accidentally loosened during maintenance. The rough idle and white smoke during cold start are classic symptoms of incomplete combustion from a malfunctioning glow plug system. Would recommend getting a full diagnostic specifically focused on the glow plug control circuit rather than just replacing parts. This could save money in the long run.

Thanks for the detailed feedback and sharing your repair experience. The situation does sound quite similar to what you faced. I will contact the service center tomorrow to have them check the wiring and connections they may have disturbed during the recent maintenance. The white smoke and rough idle during cold starts have actually gotten worse this morning. Looking back, paying 580 Euro for a proper diagnosis and complete fix of the glow plug system seems reasonable if it resolves all these cold start problems. My main concern is getting this sorted before winter fully sets in. I will make sure to specifically request they inspect the entire glow plug control module and wiring harness, not just the glow plugs themselves. Will update once I get it checked out and know what was actually causing the engine misfire and continuous preheating lamp issue. The timing right after service does make me think something must have been unintentionally disturbed during the routine maintenance.