Audi A3 Coolant Leak Linked to CAN Bus Malfunction

Had a similar issue with an A4 2009 gasoline model. The symptoms initially pointed to cooling system problems, but the root cause was actually a control module malfunction affecting multiple systems. The diagnostic trouble code indicated a CAN bus connectivity issue, which was causing false readings from the engine temperature sensors. This made the cooling system behave erratically, leading to pressure buildup and coolant loss. The problem stemmed from corroded wiring connections at the engine control unit. The communication fault prevented proper data exchange between various control modules, affecting both engine management and cooling system operation. The repair required cleaning the connection points, replacing damaged wiring sections, and reprogramming the control module. This resolved both the overheating and the check engine light issues. Not a simple fix, as it required specialized diagnostic equipment to properly identify the failing communication network components. Would strongly recommend having a thorough diagnostic scan performed, focusing specifically on the control module communication. The coolant leak might be a symptom rather than the core issue.

Thank you for sharing your experience. The car diagnostics route you took makes a lot of sense, especially with those CAN bus connectivity issues being the root cause. The control unit problems can be quite tricky to diagnose without proper tools. My mechanic also found corroded wiring but ended up replacing the entire control module since cleaning didnt work. Just wondering, do you remember roughly how much you paid for the full repair? Also, has everything been working properly since the fix, or have you noticed any new connectivity issues popping up? Our cases sound pretty similar with the false sensor readings and cooling system acting up, so Im curious about the long-term reliability after your repair.

Great to hear from you again. After my complete repair which involved fixing the connectivity issue, everything has been running perfectly with no software glitch or car diagnostics errors showing up. The communication fault was resolved by addressing a faulty cable connection, it was much simpler than replacing the entire control module like in your case. The repair bill came to 95 Euro for fixing the defective plug connection, which was causing the CAN bus problems. The key was finding a mechanic who really understood control unit diagnostics and could properly identify where the communication breakdown was happening. Since the repair, the cooling system has been working as intended with no false readings or connectivity issues. Its been about 8 months now with zero problems. Your repair approach might have cost more with the full module replacement, but it should provide excellent long-term reliability. These control unit communication errors often need different solutions depending on the exact point of failure in the system.

I wanted to give a final update on my situation. Finally took it to a specialist mechanic who deals with control unit diagnostics. The whole process was eye-opening. The mechanic ran a complete data link test and found multiple communication faults in the CAN bus system. Turns out the control unit wasnt properly communicating with the temperature sensors, causing the cooling system to malfunction. Total repair cost came to 450 Euro including parts and labor. They had to replace some wiring harnesses and reprogram the control module. The connectivity issue is now completely resolved, no more check engine light, no overheating, and the coolant system is working perfectly. What really impressed me was how they used specialized diagnostic equipment to pinpoint the exact communication fault. Been driving for about 2 weeks now with zero issues. Definitely worth spending the extra money to get it fixed properly by someone who understands these complex control unit problems.