Audi Q2 Diesel: Coolant Leak & Control Unit Fault Alert

Had similar symptoms with a 2017 Audi Q3 2.0 TDI. The diagnostic trouble codes pointed to a connectivity issue between the engine control module and cooling system sensors. The CAN bus network showed intermittent communication failures. Root cause was not the control module itself, but a wiring issue where the coolant temperature sensor harness had worn through near the engine block. This created false readings, triggering both overheating warnings and coolant system errors. The data link was essentially corrupted due to the damaged wiring. The fix required: Complete harness replacement, New coolant temperature sensor, System reprogramming, Coolant system pressure test This was classified as a serious repair since faulty temperature readings could lead to engine damage. The job took 2 full days due to the complexity of accessing the wiring behind the engine components. Important: The check engine light and control unit communication errors can be misleading. Always get the specific diagnostic trouble codes checked before replacing major components like control modules.

Thanks for sharing that detailed experience. Very similar to mine though the software glitch initially had us looking in the wrong direction. Fixed mine 3 months ago and no issues since. Did the communication fault come back at all after your repair? And would you mind sharing the repair costs? Mine ended up being quite expensive and wondering if I paid too much for the wiring issue fix. Also noticed the coolant sensor connectors needed extra protection to prevent future harness damage. Did your shop add any protective covering to the new wiring?

Good to hear you got it sorted out. After my last visit to the mechanic, the control unit communication error was completely resolved. The data link is now stable and the diagnostic trouble codes are clear. The repair was actually quite straightforward once they identified the real problem, a faulty cable connection to the component. Total cost was 95 Euro, which included the repair and testing. This seems reasonable compared to what many shops charge for CAN bus related fixes. The communication fault never returned since the repair. The wiring issue turned out to be much simpler than initially suspected, proving that thorough diagnostics are essential before jumping to expensive component replacements. The shop did add protective sheathing to prevent future wear, which was included in the repair cost. This extra protection is crucial since exposed wiring near hot engine components often leads to these types of issues. A proper fix of the underlying wiring problem is far better than repeatedly chasing intermittent communication faults through software updates or module replacements.

Let me share how my repair journey ended. Finally took it to a different mechanic who actually found the real issue within an hour using proper car diagnostics. Like you mentioned, it was indeed a wiring issue, not the control module they initially suspected. The mechanic spotted a damaged wire harness that was causing the CAN bus errors. That explained all the false readings and coolant leaks. Total bill came to 780 Euro including parts and labor. They added extra protective sleeve around the new wiring to prevent future wear. The repair took just one day and worked perfectly. No more software glitch warnings or communication errors since then. The data link is stable now and all systems communicate properly. Should have gone to this shop first, would have saved time and money chasing the wrong problem. That first misdiagnosis cost me an unnecessary control module replacement. But at least now I know better than to jump at replacing expensive parts without thorough diagnostics first.