Peugeot 307 bypass valve malfunction

I had a similar issue with my 307. The bypass valve error and overheating stemmed from an unrelated issue causing the engine to run lean. Have you checked the air intake system and fuel delivery? A faulty sensor could be causing incorrect fuel mixture, leading to both the bypass valve error and overheating. Check the mass airflow sensor (MAF) and O2 sensors for proper function. What are your long term fuel trims?

Thank you for the advice. I will check the MAF and O2 sensors as you suggested. Regarding the long term fuel trims, can you clarify what values would indicate a problem? And did the lean mixture also manifest as engine stalling or reduced fuel efficiency in your case?

If the long term fuel trim is more than +/- 10%, it suggests an issue. A lean mixture can definitely cause engine stalling and reduced fuel efficiency. In my case, the faulty sensor fooled the ECU and caused the bypass valve to actuate in an unintended way. I recommend visiting a competent workshop and having the mixture adaptation checked. Be aware that the valve itself might work as intended, but the problem might be somewhere else.

As per your suggestion, I took the car to a trusted mechanic. They found that the error was indeed a consequence of another error, which had nothing to do with the bypass valve, therefore the valve itself worked as intended. Repair cost: 0€ Thank you for your help!