VW Caddy Cooling System Failure: Wiring Diagnosis Guide

As someone with some experience diagnosing electrical issues, I had a very similar problem with my 2016 VW T6 TSI. The symptoms you describe match exactly what I encountered, coolant issues, overheating, and multiple trouble codes related to control unit communication. In my case, the diagnostic trouble codes pointed to a data link connectivity problem. After inspection, my workshop found damaged wiring near the engine control unit, where some cables had worn through due to vibration. The faulty wiring was causing intermittent communication failures between the cooling system control unit and other components. The repair involved replacing the damaged wiring harness section and checking all related control unit connections. Total cost was 95€ including diagnostic work and parts. Since the repair, all systems have been working perfectly with no more overheating or warning lights. Before suggesting specific solutions for your case, could you share: Which diagnostic trouble codes are you seeing specifically? Have you noticed any correlation between the overheating and specific driving conditions? When did these symptoms first appear? Has any recent work been done on the electrical system or cooling system? This information would help determine if your issue stems from a similar wiring issue or if there might be other factors involved.

Last service was completed just 2 weeks ago at 89678km. After reviewing your response and comparing symptoms, I am also seeing DTCs pointing to a communication fault between modules. The diagnostic report specifically shows control module timing errors similar to what you experienced. The wear pattern you described near the ECU matches what I can see when inspecting my engine bay. There is visible chafing on the wiring harness where it runs close to the engine block. This could explain the intermittent connectivity issues affecting the cooling system management. I will have the workshop inspect these specific areas and replace any damaged sections of the wiring harness. Your mention of monitoring for vibration-related damage is particularly helpful since this appears to be a common failure point across our models. The software glitch symptoms started appearing gradually over the past month, which aligns with the timeline of when I first noticed the data link problems in the diagnostic reports.

Thanks for the additional details about your Caddy. The timeline and symptoms you describe are remarkably similar to what I experienced with my T6. The gradual onset of issues combined with clear physical signs of wire chafing strongly points to a wiring-related communication fault. After fixing my car, I learned these control module communication issues often start small but quickly cascade into multiple system failures. The car diagnostics initially showed similar timing errors before the major cooling system problems developed. A key insight from my repair: the workshop found the control unit was actually functioning correctly, but the degraded wiring was corrupting the signals. This caused the cooling system to receive incorrect temperature data, leading to the overheating and pressure issues. One practical tip, while the harness is being replaced, have them install additional protective sleeving where the wires contact metal surfaces. This prevented repeat failures in my case. Also worth checking the engine mount condition, as excessive movement can accelerate wire wear. The fact your software glitch symptoms align with the diagnostic trouble codes suggests you caught this early enough to prevent permanent control module damage. This should make the repair relatively straightforward, similar to my situation.

The correlation between our issues is quite striking. Your detailed explanation of the control unit communication problems matches exactly what I am experiencing with my Caddy. The similar diagnostic trouble codes and visible wire damage make me confident we have identified the root cause. I have scheduled a workshop visit for next week and requested they specifically check the wiring harness near the ECU. Based on your experience, I will also ask them to add protective sleeving during the repair to prevent future issues. The car diagnostics data showing timing errors makes perfect sense now, especially given how the connectivity issues have been progressively getting worse. The suggestion about checking engine mounts is valuable, I had not considered how excess movement could affect the CAN bus wiring. This comprehensive approach should resolve both the immediate software glitch and prevent similar problems from recurring. Your repair cost reference gives me a good baseline for what to expect. I appreciate you sharing such specific, relevant experience that helped pinpoint these control unit communication issues. This saved me considerable time in diagnosis and likely prevented more extensive damage to the cooling system.