Thermostat Replaced
03-28-2008, 09:27 AM
#1
Senior Member
Thread Starter
Join Date: 02-01-2006
Location: lockport,ny
Posts: 1,418
Thermostat Replaced
The dealer just replaced my thermostat, which was stuck open, under warranty. What I found interesting was how the computer system(s) reacted to the thermostat failure.
About 6 weeks ago I noticed that the coolant temperature gauge would sometimes drop to zero and the DIC digital coolant temperature readout would not show a number, just "---". Then a few days later I got a SES light, which I read with my code reader (Harbor Freight, $39) and found out it was the code for "engine temperature below thermostat setpoint". I took it to the dealer and they replaced the PCM (under the hood). A few days later, the problem occured again, but no SES light. I monitored the intermittent gauge dropout over the next few weeks. Sometimes it set the SES light, sometimes not. Also noticed that when it was working, the DIC engine coolant temperature seemed to stay pretty low most of the time (130-140 degrees). Normally it got to about 190 degrees quickly and stayed there.
It sounded like an old-fashioned thermostat failure, but that wouldn't account for the gauge and DIC temperature reading dropout. Finally took it to the dealer, who after troubleshooting for a day, replaced the thermostat and now all is well.
I have the factory service manual and have read the section pertaining to SES codes. There is no situation described that would account for the PCM dropping out the Coolant temperature sensor reading if the temperature was below the thermostat operating point. Yet that's exactly what it was doing. I was baffled by the rsponse of the PCM, but happy that the problem was fixed (yay, finally have heat again!).
Yesterday I stopped at my local garage to schedule the yearly inspection required by New York State. I mentioned that I just had the thermostat replaced because I remembered that to pass NYS inspection, the car must have xx amount of miles without a SES code after the code is reset. So I scheduled the inspection for next week to be sure there were enough SES code-free miles. The mechanic then asked me" did your coolant temperature gauge reading drop out?". I said yes, it did. He said he just worked an HHR that had a SES code(wasn't a coolant problem) and the coolant temperature gauge had dropped to zero!
I just wanted to let everyone know that if their coolant temperature gauge drops to zero, it could mean that the PCM is sensing a problem (not necessarily only with the coolant temperature). I'm not sure if this is some sort of designed-in feature or whether this is some sort of bug in the software.
Steve
About 6 weeks ago I noticed that the coolant temperature gauge would sometimes drop to zero and the DIC digital coolant temperature readout would not show a number, just "---". Then a few days later I got a SES light, which I read with my code reader (Harbor Freight, $39) and found out it was the code for "engine temperature below thermostat setpoint". I took it to the dealer and they replaced the PCM (under the hood). A few days later, the problem occured again, but no SES light. I monitored the intermittent gauge dropout over the next few weeks. Sometimes it set the SES light, sometimes not. Also noticed that when it was working, the DIC engine coolant temperature seemed to stay pretty low most of the time (130-140 degrees). Normally it got to about 190 degrees quickly and stayed there.
It sounded like an old-fashioned thermostat failure, but that wouldn't account for the gauge and DIC temperature reading dropout. Finally took it to the dealer, who after troubleshooting for a day, replaced the thermostat and now all is well.
I have the factory service manual and have read the section pertaining to SES codes. There is no situation described that would account for the PCM dropping out the Coolant temperature sensor reading if the temperature was below the thermostat operating point. Yet that's exactly what it was doing. I was baffled by the rsponse of the PCM, but happy that the problem was fixed (yay, finally have heat again!).
Yesterday I stopped at my local garage to schedule the yearly inspection required by New York State. I mentioned that I just had the thermostat replaced because I remembered that to pass NYS inspection, the car must have xx amount of miles without a SES code after the code is reset. So I scheduled the inspection for next week to be sure there were enough SES code-free miles. The mechanic then asked me" did your coolant temperature gauge reading drop out?". I said yes, it did. He said he just worked an HHR that had a SES code(wasn't a coolant problem) and the coolant temperature gauge had dropped to zero!
I just wanted to let everyone know that if their coolant temperature gauge drops to zero, it could mean that the PCM is sensing a problem (not necessarily only with the coolant temperature). I'm not sure if this is some sort of designed-in feature or whether this is some sort of bug in the software.
Steve
03-28-2008, 09:46 AM
#2
Senior Member
Join Date: 06-27-2006
Location: Kingsville On
Posts: 732
The dealer just replaced my thermostat, which was stuck open, under warranty. I took it to the dealer and they replaced the PCM (under the hood).
A few days later, the problem occured again, but no SES light.Finally took it to the dealer, who after troubleshooting for a day, replaced the thermostat and now all is well.Steve
A few days later, the problem occured again, but no SES light.Finally took it to the dealer, who after troubleshooting for a day, replaced the thermostat and now all is well.Steve
wonder how much that cost GM for a $5 part
09-09-2011, 07:01 PM
#5
Platinum Member
Join Date: 04-09-2006
Location: Vancouver, BC, Canada
Posts: 7,037
OP - your description is spot on. A number of us have already been through the thermostat problem - a search through the forums here will bring up the procedure needed to replace the thermostat yourself as well as descriptions of the reasons for the blanked out display etc.. I don't know if you noted or noticed it, but the A/C is also disabled under certain circumstances.
11-28-2011, 10:43 AM
#7
Join Date: 10-05-2011
Location: atlanta
Posts: 2
I had the exact same problem. In fact, I had my thermostat replaced 3 times over the last year. Check engine light and error code was indicating that temperature was not being reached fast enough. I had my doubts about a faulty thermostat. I couldn't imagine having that many faulty thermostats.
The problem for me seems to be solved. Its NOT the thermostat. The problem was actually a bad Engine Coolant Temperature sensor. The Coolant sensor was sending false (low) temp readings. The Fault code was then tripped. Since I had the coolant temp sensor replaced. What was fooling the Mechanic is that the service manual says to replace the thermostat.
My symptoms were:
1. Temp gauge reading ---
2. No A/C
3. Fault code indicating temp not reaching correct temp quick enough (p0128)
The problem for me seems to be solved. Its NOT the thermostat. The problem was actually a bad Engine Coolant Temperature sensor. The Coolant sensor was sending false (low) temp readings. The Fault code was then tripped. Since I had the coolant temp sensor replaced. What was fooling the Mechanic is that the service manual says to replace the thermostat.
My symptoms were:
1. Temp gauge reading ---
2. No A/C
3. Fault code indicating temp not reaching correct temp quick enough (p0128)
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