Check Engine light came on

[vbros7]

Hello, my check engine light came on yesterday so i went to Auto Zone and the guy told me that my coolant level was low, or i may need a new thrermostat. How do u know if you need a new thermostat, what do i need to look for. I have a 02 Grand Prix GT with about 50,000 miles on it.

Thanks in advance guys!

[grandprixgtx00]

low coolant wouldnt throw a SES light, it would just make your low coolant light come on. neither would a bad T-stat.

if you needed a T-stat, your car would either run real hot, or real cold...depending on whether the T-stat is stuck open or closed.

I would have someone else hook a scanner up and see why the SES light is on. do you notice any difference in driveablilty??

[vbros7]

No, i havent noticed anything different at all. I noticed after i was leaving auto zone the temp gage was starting to go up, but once i started going and getting cold air back into the engine it went back down again. I might go back to auto zone and have them check the code again, some of the people there i just cant trust, it seems like they dont know anything about cars. Do u think it would just be woth spending 10 dollars on a new thermostat, and seeing how that goes?

[grandprixgtx00]

well, if the SES light is on...i really dont think a T-stat is gonna fix anything. if you say that the temp started rising a little, and it would make you feel safe to put a T-stat in, then go ahead. but like i said, i dont think its gonna fix the SES light.

i would just bring it back and scan the codes again. once you get a code pulled out of the system...let us know what it is. i we may be able to help you out then.

[vbros7]

Ok i will get back to u in a couple of days when i get it re scanned

[phjohnso]

i had the same thing, the problem was the engine wasn't getting warm enough within a set time. I changed out the therm to a fail-safe. No more check engine light

[grandprixgtx00]

Originally Posted by phjohnso

i had the same thing, the problem was the engine wasn't getting warm enough within a set time. I changed out the therm to a fail-safe. No more check engine light

??

Never heard of such a thing...

[phjohnso]

i think the error code was P0128 for coolant temp low - apparently the old thermostat failed in the open position so the engine didn't fry.

[richtazz]

A stuck open t-stat on a GM OBD-II car will trigger a code P0128-"ECT reading below thermostat regulating temperature".

This will cause poor performance and mileage due to the PCM not going into closed loop mode. It will also cause a lack of heat due to the coolant not being allowed to come up to temp before the t-stat opens. It sounds like a new t-stat should fix your issue as long as you're not losing or low on coolant. If that's the case you could have other issues that led to the failed t-stat.

[grandprixgtx00]

[quote=richtazz]A stuck open t-stat on a GM OBD-II car will trigger a code P0128-"ECT reading below thermostat regulating temperature". quote]

hmm...nice thing to know. I've never heard of a T-stat throwing a SES light. learn something new everyday i suppose