# Engne Light/cooling thermostat



## trentwill83 (Oct 20, 2009)

i took my car into pep boys yesterday because my car has been givin me the check engine light on and off for about a week. it will come on for about three day then go away. so i have them check it out and they get a code that says it is the cooling thermostat. so the guy tells me either it is the termostat or the sensor of engine temp. to get the thermostat replaced will cost about 180. to get a full diagnostic will cost 90. and he didnt mention anything about the sensor. anybody have any clue why the engine light would come on and off by itself over a few days?? and what would be the best way of going about getting it fixed?


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## 6QTS11OZ (Mar 27, 2005)

Those prices are ridiculous. The thermostat is easy as hell to change. 

My check engine light comes on because my coolant temp is too low. I have a 160 degree stat and when the outside temp is 40 degrees or lower and the coolant temp is around or below 163 degrees the light stays on. If the coolant temp rises and stays above that (normal operating temp) the light will go out even though the code is still stored in the ECM. Until I have the low coolant setting lowered in my ECM I will always get a low coolant temp light when it's cold out. In the summertime the light stays off and I forget all about it.

First you need to do is go to AutoZone and have them scan the code for free. Or you can buy a nice code reader and be done with those crooks charging you to do a simple scan. Once you know what the code is then come back and let us know so we can have something to go off of.


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## jpalamar (Jul 22, 2008)

I had the same issue and it was my t-stat. It was $15 to fix. Took me all of about 20 minutes to replace and then top off my DEX-COL. Once you reaplce it, it will take a drive cycle or 2 of running at proper temps but your CEL should go down.

There is no way I would pay that.


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## Poncho Dan (Jun 30, 2009)

I was going to suggest doing the Mode & Set trick (Holding "mode" and "set" while turning the key to the "on" position), but after looking in the Helms factory repair manual, it's saying something about having to read the digits shown backwards.
Like this:
32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17
16 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01

That really threw me for a loop, and now I'm really confused as to how to read it... the book isn't all that clear beyond telling you to read it backwards.


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## 87GN06GTO07IRL (Aug 10, 2009)

In twelve years of being a mechanic i ve never heard of a thermostat causing a check engine light, but as we all know, anythings possible with these cars! If the cel comes on, its from a faulty electrical sensor of some sort or wiring or connector for that sensor more times than not. If you have a ect (engine coolant temperature sensor) out of range, its your coolant temp sensor more than likely if your not overheating or very low on coolant. These operate off of resistance readings. When they're cold they have more. Run a quick ohms test on the sensor and do a search for the proper specs, i dont know them off hand. Some times they can be fixed by cleaning them. Over time they ll acquire a build up and set a code and a cleaning will fix this. If not the sensors are cheap, easy to access, and quick to change. Also test the connector to make sure you have continuity.

I ran a 160 t stat on a stock tune and it never set a code. Might want to do an ohms test too, might need to be cleaned or replaced. Once i got a Predator i lowered the fan settings also and still didnt set a ect code.


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## jpalamar (Jul 22, 2008)

^ bad t-stat if it doesn't fully close will not allow the engine to get to proper running temps. Not hitting proper operating temps will cause a CEL.


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## Rukee (Feb 8, 2007)

^^ Right, if it doesn't hit normal operating temp within a set amount of time, the cel light may come on.


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## 6QTS11OZ (Mar 27, 2005)

06gtoin216 said:


> In twelve years of being a mechanic *i ve never heard of a thermostat causing a check engine light*, but as we all know, anythings possible with these cars! If the cel comes on, its from a faulty electrical sensor of some sort or wiring or connector for that sensor more times than not. If you have a ect (engine coolant temperature sensor) out of range, its your coolant temp sensor more than likely if your not overheating or very low on coolant. These operate off of resistance readings. When they're cold they have more. Run a quick ohms test on the sensor and do a search for the proper specs, i dont know them off hand. Some times they can be fixed by cleaning them. Over time they ll acquire a build up and set a code and a cleaning will fix this. If not the sensors are cheap, easy to access, and quick to change. Also test the connector to make sure you have continuity.
> 
> I ran a 160 t stat on a stock tune and it never set a code. Might want to do an ohms test too, might need to be cleaned or replaced. Once i got a Predator i lowered the fan settings also and still didnt set a ect code.


Uhh... yes it will.



jpalamar said:


> ^ bad t-stat if it doesn't fully close will not allow the engine to get to proper running temps. Not hitting proper operating temps will cause a CEL.





Rukee said:


> ^^ Right, if it doesn't hit normal operating temp within a set amount of time, the cel light may come on.


You guys are right!

That's exactly what I explained in my first post.


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## Poncho Dan (Jun 30, 2009)

Happened in my Grand Am a few years ago. The answer was a new thermostat.


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