Bad Temp Sensor or Bad Thermostat. How can I tell? Need help

[99GST]

I am getting a CEL # PO125 which is Insufficient Cooling Temp for Closed Loop Control.

DarkOne was nice enough to tell me that I probably have a bad coolant temp sensor, or a bad thermostat. Either my coolant is not getting hot enough for the ECU to switch into closed loop, or my coolant temp sensor is misreporting the temp and the same result happens. So my car is stuck in warm-up mode, and it will run nasty rich trying to warm up the car.

How do I tell which is bad? The coolant temp sensor or the thermostat? The factory temperature gauge is where it should be just below the center mark.

Any ideas or suggestions? Please let me know, as I am clueless on this one.

Thanks,
Nathan

 

[Rx3]

1) Wrong forum

2) search button : http://www.dsmtuners.com/forums/showthread.php?s=&threadid=16100&highlight=Coolant+affects+fuel

there are a few more.


3) Have you ever changed your thermostat? IF so what temp rating (in degrees) did you install? The ECU wants 190+ coolant temps. Any less and it will run on its start up(cold engine) fuel maps.

I live in a cold state, (at least right now its freezing) and my temps barely crack 190 on some days. Most days I'm about 210 or so. But you live in Kentucky. I'm assuming it is a bit warmer than Buffalo, soI'm not sure why you would be having this problem. Another thing to check. Are you using watter wetter? If you are, it might be a good idea to flush it and use regular coolant during the cold months. The extra 10 degrees or so that watter wetter lowers your coolant temp might be counter productive in the cold when your ECU is looking for a certain degree reading to switch maps.

Also check O2 sensors (can't hurt)

 

[Stock90GSXT]

A thermostat is cheap enough, and easy enough to just buy it and do it. Is your heater getting hot?..If its not, check your coolant level, if thats ok. Replace thermostat. I think the thermostat is doing its job. The car is getting to its desired temp. Get the code cleared and see if the engine light comes back on. I can almost bet it is the coolant temp sensor. You can check that with a DVOM (OHM METER). As the car I think gets warmer, the resistance goes down. Or vise versa...Im not 100 percent positive on that. Check the service manual on how to check that.

 

[99GST]

Originally posted by Rx3


3) Have you ever changed your thermostat? IF so what temp rating (in degrees) did you install? The ECU wants 190+ coolant temps. Any less and it will run on its start up(cold engine) fuel maps.

I live in a cold state, (at least right now its freezing) and my temps barely crack 190 on some days. Most days I'm about 210 or so. But you live in Kentucky. I'm assuming it is a bit warmer than Buffalo, soI'm not sure why you would be having this problem. Another thing to check. Are you using watter wetter? If you are, it might be a good idea to flush it and use regular coolant during the cold months. The extra 10 degrees or so that watter wetter lowers your coolant temp might be counter productive in the cold when your ECU is looking for a certain degree reading to switch maps.

Also check O2 sensors (can't hurt)

I have never changed the thermostat. I plan on swinging by Autozone to pick up a t'stat and gasket. I am pretty positive that my coolant temps are around 170. I will double check with datalogger tonight.

Kentucky has been pretty cold these last few months. FOr exmaple, over xmas it was colder here than NYC. I am not using Water Weatter, just straight up anti-freeze. However, I am going to flush it out again and pour in a fresh batch. The 2nd O2 sensor, in the exhaust, wouldnt cause this CEL. My first O2 was replaced about 17xxxx miles ago. It should still be okay. I cant imagine it would have gone bad. But, we will have a look.

What ever came of your problem? Was it your thermostat or coolant temp sensor?

Thanks for your help.
Nathan

 

[99GST]

Originally posted by Stock90GSXT
A thermostat is cheap enough, and easy enough to just buy it and do it. Is your heater getting hot?..If its not, check your coolant level, if thats ok. Replace thermostat. I think the thermostat is doing its job. The car is getting to its desired temp. Get the code cleared and see if the engine light comes back on. I can almost bet it is the coolant temp sensor. You can check that with a DVOM (OHM METER). As the car I think gets warmer, the resistance goes down. Or vise versa...Im not 100 percent positive on that. Check the service manual on how to check that.

I am getting one today. Yes my heater is getting hot. My coolant level is good, but the overflows tank is really low. So, I will fill that up. I have reset the CEL twice now, and it has come back on. It came on by the next day after resetting it.

I too have a feeling that it is the coolant temp sensor, but since the thermostat is cheaper and easier to check, I will do that first.

Thanks for your help.
Nathan

 

[L2RTSiAWD]

Moved to repair forum

 

[Rice Killer]

I can almost guarantee it's your Engine Temp sensor if your CE light is coming on. For a 1g this sensor goes in the bottom of the thermastat housing, I just replaced mine and I had the same CE light (21 coolant temperature) so i know that's problem. Those are not cheap either $35 from Napa maybe a little cheaper at a dealer with a DSM discount. It's real easy to replace
Good Luck

 

[Stock90GSXT]

Originally posted by Rice Killer
I can almost guarantee it's your Engine Temp sensor if your CE light is coming on. For a 1g this sensor goes in the bottom of the thermastat housing, I just replaced mine and I had the same CE light (21 coolant temperature) so i know that's problem. Those are not cheap either $35 from Napa maybe a little cheaper at a dealer with a DSM discount. It's real easy to replace
Good Luck

Well, whats sad..is that 99 percent of us are wrong. I looked it up today. And you must have got that code at Autozone. The code is right, but the information we are giving him is wrong. What sucks is that it has nothing to do with the coolant at all. It could be your FRONT 02 sensor, or a fuel injector. I looked it up on Mitchel -On Demand.

 

[Rice Killer]

I dont know what your talking about but (21 coolant temperature) is the code I got and it was the engine temperature sensor. Maybe you have another problem I havent heard of before. But that's what was wrong with my car.

 

[Rx3]

Originally posted by Rice Killer
I dont know what your talking about but (21 coolant temperature) is the code I got and it was the engine temperature sensor. Maybe you have another problem I havent heard of before. But that's what was wrong with my car.

99 GST's code is 0125. Not 21.

Originally posted by Stock90GSXT


Well, whats sad..is that 99 percent of us are wrong. I looked it up today. And you must have got that code at Autozone. The code is right, but the information we are giving him is wrong. What sucks is that it has nothing to do with the coolant at all. It could be your FRONT 02 sensor, or a fuel injector. I looked it up on Mitchel -On Demand.

99GST pulled his code with the pocketlogger, so I'm not sure where Autozone comes in.... unless that comment was meant for RiceKiller?

Do you have a link for that? I'd like to see what you are talking about

Originally posted by 99GST


What ever came of your problem? Was it your thermostat or coolant temp sensor?

Thanks for your help.
Nathan

I flushed my coolant, put in a fresh batch with no water wetter. Now my temps even on cold days get up to 210-215 degrees once the car warms up. I haven't gotten that error/CEL ever since. I figure after it gets warm again, I'll throw the water wetter back in.

 

[Stock90GSXT]

I got my information on Mitchell On Demand. Its a repair software for 83-2002 vehicles. And believe it or not, thats what they say to check. Now the service manual may say otherwise. I hav'nt seen the actuall mitsu service manual. They should coincide with each other.

 

[99GST]

I went ahead and purchased a new t-stat from autozone. I believe it was made by STANT. It was cheap and it is an easy pop in out deal. So I will do that this weekend.

I had changed out my front O2 sensor about 17k miles ago. I cant imagine that this would be the problem. Plus with the error code I received it just doesnt make any sense.

Yesterday was pretty darn warm for us, about 50 degrees. On my way home from work, I ran a datalog. Once the car was warm the coolant temperature was only 185-196 degrees. Therefore, it is either my t-stat or the coolant temp sensor.

After this weekend, I will let everyone know if the t-stat helped.

Thanks again for all of your replies and suggestions.
Nathan

 

[Groomz]

I live in Texas and it gets pretty hot during the summer here. Should I go with a 180 degree thermostat or the factory 195?

 

[99GST]

Originally posted by Groomz
I live in Texas and it gets pretty hot during the summer here. Should I go with a 180 degree thermostat or the factory 195?

I would just get the standard 195 tstat. There can be alot of problems if you get the 180 tstat. Not to mention most of the problems that may arise with a 195 will also arrive with a 180. So, why not just get a nice OEM part.

But that is just my litte $0.02

Later.
Nathan

 

[stockmkt8r]

Originally posted by 99GST
I went ahead and purchased a new t-stat from autozone. I believe it was made by STANT. It was cheap and it is an easy pop in out deal. So I will do that this weekend.

I had changed out my front O2 sensor about 17k miles ago. I cant imagine that this would be the problem. Plus with the error code I received it just doesnt make any sense.

Yesterday was pretty darn warm for us, about 50 degrees. On my way home from work, I ran a datalog. Once the car was warm the coolant temperature was only 185-196 degrees. Therefore, it is either my t-stat or the coolant temp sensor.

After this weekend, I will let everyone know if the t-stat helped.

Thanks again for all of your replies and suggestions.
Nathan

Sooo, what ever happened??

 

[99GST]

Originally posted by stockmkt8r


Sooo, what ever happened??

Wow, this has been a long time. I replaced the tstat. Everything is peachy now

Thanks,
Nathan