VW Up Engine Overheats with Coolant Leak, Control Unit Issue

Had a similar issue on a 2017 VW Polo TSI. The symptoms started exactly the same, engine overheating, coolant leaking, and persistent check engine light. Initial diagnostic trouble code scan revealed a communication fault between the engine control unit and cooling system sensors. The root cause turned out to be both mechanical and electronic. A corroded wiring connector at the coolant temperature sensor was disrupting the CAN bus signals, causing the control module to receive incorrect temperature readings. Additionally, the water pump had developed a crack, explaining the coolant leak. This wasnt a simple software glitch but rather a connectivity issue combined with mechanical failure. The repair required: Replacement of the coolant temperature sensor connector, New water pump installation, Complete system diagnostic reset, Coolant flush and refill The job was quite serious since continuous overheating could have caused engine damage. Would strongly recommend getting a proper diagnostic scan first to identify if theres any control module communication errors before assuming its purely a mechanical problem. For a proper diagnosis, look for a shop with VW-specific diagnostic equipment that can properly read all control unit parameters, not just basic OBD codes.

Thanks for the detailed insight. The symptoms and repair process you described match my situation perfectly. My car is currently at a different shop doing a complete car diagnostics check. They mentioned similar concerns about the data link communication between sensors. Would you mind sharing how much the total repair cost in your case? Also, did you experience any related issues after the fix was completed? Just want to gauge if I should anticipate any follow-up problems.

Since getting my VW fixed, everything has been running perfectly with no further cooling issues. The car diagnostics performed at the new shop uncovered that the control unit communication error was indeed caused by a damaged wiring issue, much simpler than initially feared. The faulty connection was affecting how the temperature data was being transmitted to the main control unit. The repair was straightforward, they fixed the cable connection which restored proper data link communication between components. Total cost came to 95€ for the wiring repair. Much more reasonable than the complete system overhaul I was worried might be needed. No follow-up problems in the months since the fix. The engine temperature now reads normally, and the check engine light has stayed off. Would recommend getting any similar symptoms checked promptly by a shop with proper diagnostic tools to catch these kinds of wiring issues before they cause bigger problems.

I finally got my car back from the new mechanic and the issue has been fully resolved. The problem turned out to be very similar to what was initially suggested, a connectivity issue between the control module and temperature sensors, along with a minor coolant leak. The total repair came to 380€ which included: Fixing damaged sensor wiring, Replacing a cracked coolant hose, Full system diagnostic scan, Coolant system pressure test, Fresh coolant refill The CAN bus signals are now reading correctly and the engine temperature stays perfectly normal. No more check engine light or coolant leaks. Feel much better knowing it wasnt a major mechanical failure or software glitch in the main control unit. Really glad I switched to a different shop. Their diagnostic equipment picked up the exact issue right away and their communication throughout the repair process was excellent. The car runs better than it has in months.