A3 Diesel Glow Plug Unit Failure Causing Cold Start Issues

My 2018 A4 diesel had nearly identical symptoms. The constant preheating indicator and engine misfire during cold starts pointed to a faulty glow plug control module. The heating element was receiving incorrect voltage due to corroded wiring connections at the control unit. The vehicle stalling and rough running were caused by improper combustion, as the glow plugs weren't reaching optimal temperature. The smoke under acceleration is typical when glow plugs fail to properly heat the combustion chamber. The repair involved: Testing each glow plug individually, Replacing the control module, Cleaning connection points, Installing new wiring harness This was a significant car maintenance job requiring specialized diagnostic equipment. The issue can damage injectors if left unaddressed, leading to more expensive repairs. Getting it fixed promptly prevents further engine damage and poor fuel economy. Would recommend having a full diagnostic test done specifically focused on the glow plug system and control module before attempting any repairs. The symptoms match a control unit failure rather than individual glow plug issues.

Actually had this exact problem last winter with my A3. The engine light came on and I had similar issues during cold starts. The mechanic found the glow plug control unit was faulty and causing the heating element system to malfunction. After replacing the control unit and doing some engine diagnostics, everything went back to normal. The engine misfire symptoms disappeared completely and cold starts are smooth now. Been about 8 months since the repair and no issues have come up. Would be helpful to know what you ended up paying for the fix. My car maintenance costs have been higher than expected this year, so curious how the repair costs compared.

Following up on the glow control unit problems, got it fixed last week and the repair was much simpler than expected. The mechanic found a damaged cable connection at the control module that was causing the malfunction. A thorough diagnostic test revealed no issues with the individual glow plugs themselves. The repair only came to 95 Euro to fix the faulty wiring. Much better than initially feared, since complete control unit replacement can cost significantly more. The engine light cleared right after the repair and cold starts are perfect now. No more engine misfire or smoke issues during acceleration. Regular car maintenance helped catch this early before it could cause problems with the injectors or other components. Getting that diagnostic test done promptly was key to identifying the simple wiring fix rather than assuming worst-case scenarios.

Thanks for all the feedback on my glow plug control unit issue. Finally got it sorted at a new mechanic last week. After running a diagnostic test, they found both a faulty control module and some damaged wiring, basically what you all described. The total repair came to 485 Euro, more than the simple wiring fix but less than I feared. They replaced the control unit, fixed the connections, and checked all the glow plugs. The car maintenance receipt shows they also cleaned the connection points as a preventive measure. The vehicle stalling and rough starts are completely gone now. No more check engine light or smoke under acceleration. Cold morning starts are smooth again. The new mechanic did great work and took time explaining everything. Really glad I got it fixed before winter hits and before it could cause more engine damage. Thanks again for helping identify the likely cause. Having your similar experiences made me more confident pushing for the right diagnostic tests and repairs.