Code PO128

JOE1953

MEMBER
2006 SATURN ION
2.2L
4 CYL
4WD
AUTOMATIC
143,000 MILES

Engine light came sometime when driving I had the computer scanned and the code is PO128, and they said the thermostat is going bad will you explain this code PO128 do I need to replace the thermostat? The engine is not overheating but I don't think I am getting the gas mileage I once was. Will a bad thermostat decrease the gas mileages?

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

This would be a thermostat if the engine is truly not reaching operating temp but that is unlikely. So while it could cause the issue, this code is telling you that based on the amount of air that comes into the engine that it expects the engine to be warmed up but it is not showing that it is.

More then likely this is a coolant temp sensor. So let's run through this testing attached below using these guides to complete this testing:

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Please see the attached info and let us know what questions you have.

Thanks

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