Subaru Forester Cooling System Failure & ECU Alert

Had similar problems with my 2013 Subaru Outback diesel. The symptoms match what turned out to be a failed ECU control unit combined with a damaged wiring harness near the radiator. The constant overheating despite new coolant points to a communication fault between the temperature sensors and the ECU. In my case, moisture had corroded the wiring connection, creating a connectivity issue that caused false temperature readings. The fix required: Complete diagnostic scan of all control modules, Replacement of damaged wiring harness, Reprogramming of the engine control unit, Installation of new temperature sensors This was indeed a serious issue requiring specialized diagnostic equipment. The connectivity issue caused the ECU to receive incorrect data, leading to improper engine management and overheating. Key warning signs were: Persistent check engine light, Inaccurate temperature readings, Control unit error codes, Coolant leaks near electrical connections Recommend having the wiring harness thoroughly inspected, particularly around the coolant system connections. A software glitch might also be involved, but physical wiring issues should be ruled out first.

Thanks for sharing those details about the ECU and wiring harness problems. My Forester had almost identical symptoms last year. After running the car diagnostics, they also found issues with the CAN bus system and corroded connections causing those control module errors. Just wondering, how much did the complete repair end up costing you? And has the car been running fine since the fix, or have you noticed any other data link issues popping up? Would be helpful to know what to expect if I need similar repairs done.

The complete repair job was less extensive than initially feared. The main problem turned out to be a faulty connection causing the control unit communication error, which the mechanic resolved by fixing a damaged cable harness plug. Total cost was 95€ for the repair, much lower than expected considering the symptoms. Since addressing the connectivity issue last month, the car has been running perfectly with no more data link problems. The CAN bus system is now communicating properly, and all control module errors have cleared completely. Temperature readings are stable and accurate, proving it was indeed just a physical connection problem rather than a more complex software glitch. Worth mentioning that catching these communication fault issues early likely prevented more expensive damage. Regular diagnostic scans can help spot these problems before they escalate into major repairs.

Thanks for the input. Wanted to give an update on how things turned out with my Forester. Finally took it to a specialized diagnostic center after getting these suggestions. The mechanic found exactly what was described, corroded wiring connections affecting the control module communication. They performed a complete car diagnostics scan which revealed multiple CAN bus errors. The main culprit was moisture damage near the radiator harness that was disrupting signals between the control units. Repair involved replacing some wiring sections and cleaning the connection points. Total cost came to 420€ including diagnostics and parts. Been three weeks now and the car runs perfectly, no more overheating, no warning lights, and all control module readings are normal. Definitely worth getting proper diagnostics instead of just replacing parts out of nowhere like my previous mechanic did. Really glad I got this sorted before it caused more serious damage. Those original 800€ repairs were basically wasted since they never addressed the actual communication fault causing the problems.