VW Bora Engine Overheating Due to Control Unit Malfunction

Had similar problems with a 1997 VW Golf GTI last summer. The symptoms match exactly what you describe, engine overheating, coolant leaks, and persistent check engine light. Initial diagnostic trouble codes pointed to a control module malfunction. After running car diagnostics, it turned out the connectivity issue was more complex than just a cooling system problem. The data link connector between the engine control module and cooling system sensors had corroded, causing false readings. This made the system think the engine was running cooler than actual temperature. The control module was getting incorrect data, leading to improper coolant flow management. When the mechanic investigated the wiring harness, several damaged pins were found in the main connector. This is a serious issue since it affects multiple vehicle systems and can cause engine damage if left unrepaired. A full inspection of the CAN bus system revealed additional communication faults between modules. The root cause was water damage to the main wiring harness, affecting various control unit connections. Required complete replacement of the affected wiring sections and connectors to restore proper system communication. Would strongly recommend getting a full diagnostic scan focused on the control module communication before assuming its just a cooling system issue.

Thanks for the detailed explanation of your Golf GTI repair. This helps a lot since my Bora seems to be showing identical symptoms. The wiring harness issue makes total sense given how the control unit is behaving. Mind sharing what the final repair cost was for fixing the data link connectivity and harness replacement? Also curious if youve had any recurring diagnostic trouble codes or cooling issues since the repair was done?

Had the repair done at a local garage and pleased to report zero control unit communication errors since then. The mechanic found the exact issue, a faulty cable connection that was disrupting the data link signals between modules. Total bill came to 95€ for fixing the defective component connection. No software glitches or cooling problems in the months following the repair. The diagnostic trouble codes that were constantly appearing have completely cleared up. The CAN bus system is now working exactly as it should, with all control modules properly communicating. This was definitely the right fix rather than replacing major cooling system parts. Would suggest getting your Bora checked specifically for similar connection issues, since the symptoms match so closely with what my GTI experienced.

Finally got the Bora checked out by a specialist shop yesterday. You were spot on about the wiring issues. The mechanic found multiple corroded connections in the main harness affecting the control module readings. The repair took about 4 hours. They had to trace all the affected wiring and replace several damaged connectors. Total cost came to 280€ including parts and labor. More than I hoped but less than replacing major cooling components. Car diagnostics confirmed the CAN bus communication is now restored. All control unit signals are reading correctly and the engine temperature stays normal. No more coolant leaks or check engine warnings. Really glad I looked into the electrical side rather than just replacing cooling parts. The software glitch symptoms completely disappeared once they fixed those bad connections. Should have checked the wiring earlier instead of assuming it was just a mechanical problem.