VW Touran Coolant Leak Points to ECU Communication Issue

Having dealt with a similar issue on my 2013 VW Tiguan 2.0 TSI, I can share my experience as someone with moderate car repair knowledge. The symptoms you describe match what I encountered, engine overheating and coolant leaks. Initially, I thought it was just a simple coolant leak, but the workshop discovered a communication fault between the engine control unit and the cooling system sensors. The diagnostic trouble codes pointed to a wiring issue near the coolant temperature sensor. The mechanic found corroded pins in the sensor connector, which caused incorrect temperature readings. This made the cooling system behave erratically, leading to pressure buildup and coolant loss. The fix involved cleaning the connector, replacing damaged wiring, and performing a complete diagnostic scan to ensure proper communication between all control units. Total cost was 95€ for parts and labor. To provide more specific guidance for your case, could you share: Have you scanned for diagnostic trouble codes? Does the overheating occur more during city driving or highway speeds? Are there any other warning lights besides the check engine light? Has the coolant been changed recently? This would help determine if your issue is similar to what I experienced or if there might be other underlying problems.

Had mine serviced last week at 95679km. The coolant leak continued even after replacing the thermostat. After running diagnostics, they found corrupted data in the control module affecting temperature readings. Once they reprogrammed the module and verified proper CAN bus communication, the overheating issues stopped. The diagnostic trouble codes also revealed a failing coolant temperature sensor that was sending incorrect signals through the data link. Total repair cost was around 450€ including parts and labor.

Thanks for the update on your Touran repair. Your findings really mirror what happened with my Tiguan after digging deeper. While my initial connector cleaning helped temporarily, the root cause was indeed more complex, involving corrupted control module data. The CAN bus diagnostic results showed similar communication faults between the engine control unit and temperature sensors. The coolant temperature sensor was sending erratic signals through the data link, causing the system to build excessive pressure. A full control module reprogramming along with sensor replacement finally resolved my overheating issues too. The repair costs were in the same range, around 430€ for the complete fix. The diagnostic scan afterward confirmed proper communication between all components. These temperature control issues seem to be a weak point in our engine series. For others reading this thread, if you experience similar symptoms, make sure your mechanic performs a thorough car diagnostics scan of the entire cooling system communication network, not just basic troubleshooting. Glad you got it sorted. How has the cooling system performance been since the repair? Have you noticed any changes in engine temperature readings?

Thanks for following up about the Touran cooling system repair. Since getting the control module reprogrammed and fixing the CAN bus communication issues two weeks ago, the engine has been running at normal temperature. The coolant level stays consistent now with no more leaks. The diagnostic trouble codes were spot on, it definitely needed both the software fix and new temperature sensor to resolve the communication fault. The mechanic showed me the data readings before and after, and the difference is clear. Previously the system was getting totally wrong temperature signals through the data link. I track my engine temps during my commute and they stay perfectly steady now. No more overheating warnings or check engine lights. The 450€ repair cost was worth it to fix what turned out to be a complex wiring issue affecting multiple systems. For anyone else with similar symptoms, have your mechanic check both the hardware and software sides of the cooling system. A simple leak could actually be caused by a software glitch in the control modules.