VW Transporter Overheating & Control Module Failure Alert

Had a similar situation with a 2009 VW Golf GTI. The symptoms matched exactly, coolant leaks, overheating, and control module warnings. The diagnostic trouble codes pointed to a communication fault between the engine control module and the cooling system sensors. The root cause was a combination of issues. First, there was a degraded wiring harness connecting to the coolant temperature sensor. The CAN bus network wasnt receiving accurate temperature readings, triggering false overheat warnings. Second, the actual coolant leak was coming from a cracked coolant flange, which is a common failure point on these engines. The repair required: Replacing the wiring harness, Installing a new coolant temperature sensor, Replacing the coolant flange, Performing a control module software update This was definitely a serious repair that needed immediate attention. Continuing to drive with these symptoms risks major engine damage. The control module issues were actually a blessing in disguise, alerting to the problem before catastrophic overheating occurred. Would strongly recommend getting the cooling system pressure tested first to locate the leak point, then having a full diagnostic scan to check for any communication faults in the sensor network.

Thanks for sharing your experience. This matches what happened with my Transporter too. The data link errors in the diagnostic scan were what initially threw me off, making me think it was just a software glitch. Ended up being both a bad sensor and actual cooling system problems. Just curious, do you remember roughly what the total repair cost was for all that work? Also, has everything been running smoothly since getting it fixed? My repair was about 6 months ago and I sometimes still notice the control module acting a bit strange on cold starts.

After my repairs were completed 6 months ago, the control unit communication error was fully resolved. The mechanic found and fixed a faulty cable connection that was causing the connectivity issue with the cooling system sensors. Total cost was just 95€ for the wiring repair. The diagnostic trouble codes no longer appear and the CAN bus network is communicating properly with all sensors. Temperature readings have been spot-on since the fix, with no more software glitches or false warnings. Regarding your cold start concerns, could be worth having the control unit checked again, as intermittent sensor issues often surface in cold conditions. My VW Golf GTI has been running perfectly since the repair, no more coolant leaks, accurate temperature readings, and zero warning lights. The key was finding a shop that properly diagnosed both the electronic and mechanical aspects of the cooling system.

Finally got the repairs done last week after finding a certified VW specialist. The car diagnostics showed exactly what you mentioned, both electronic and mechanical problems. The mechanic discovered the wiring issue affecting the temperature sensors, plus a failing water pump that was causing the coolant leaks. Total bill came to 780€ including parts and labor. More than expected, but worth it to have everything fixed properly. The control unit is now working perfectly and engine temperature stays steady. No more puddles under the car either. Feels good to have this sorted after months of uncertainty. The shop actually showed me the corroded wiring they replaced, definitely not something I could have fixed myself. Really appreciate the guidance from everyone here. Sometimes these communication faults can mask bigger problems that need professional attention.