Celica Overheating Bypass Valve Error

Greetings. I had a similar situation arise with my old Saab 9-3, albeit a different make. An error was thrown, and the engine overheated; in my case, this was due to an auxiliary problem. The error about the bypass valve might not be the root cause, but rather a consequential error due to another issue. Have you observed any other symptoms, such as engine stalling, coolant leaks, power loss, or decreased fuel efficiency?

Thanks for the insight! Engine stalling? I've noticed it stumbles a little sometimes at idle. Coolant seems okay. I haven't really noticed a power loss, and fuel efficiency seems normal. What was the 'auxiliary problem' in your Saab that caused the bypass valve error?

The auxiliary problem was a faulty sensor; in the Saab it was a crankshaft position sensor. It caused a cascade of errors that eventually triggered a bypass valve notification, even though the valve itself was operating correctly. Given that you're experiencing engine stumbling in addition to the overheating and bypass valve error, I suggest consulting a trusted workshop. The error memory is only ever as good as the sensors sending it data; a diagnostic check could reveal the true source of the problem.

Thanks so much for your help! I took it to a shop, and you were spot on. It wasn't the bypass valve at all. It turns out a different sensor was malfunctioning, causing the bypass valve error and the overheating as a consequence. The cost to fix the consequential errors was 0€ – the sensor was the true issue. Appreciate you pointing me in the right direction!