Coolant temperature gauge not working?

Tiny
OAKDALEKID
  • MEMBER
  • 2007 CHEVROLET HHR
  • 98,568 MILES
I noticed last night that my engine lite was on. I also noticed that my temp gauge was staying on cold, but the car is not over heating. The heater works fine, so does the A/C. I use the computer read out on the sterring wheel and every thing reads perfect except the temp read out that is blank. The mileage is working the mile I have traveled is working the average speed is working, the miles per gallon is working. But the temp read out is not. Anything to do with the temp is is not working, but the car is running fine. What is the problem. Even the oil read out is working. Is this something that is major?
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Wednesday, May 29th, 2013 AT 8:35 AM

11 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Hello,

It sounds like the coolant sensor has shorted but to be sure lets run the codes this guide will help with instructions in the diagrams below to help you locate and replace the sensor.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.
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Wednesday, May 29th, 2013 AT 8:37 AM
Tiny
HOCNGUYEN
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  • 2 POSTS
I had to get a new coolant sensor all fixed!
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Friday, August 9th, 2019 AT 6:00 PM
Tiny
ADRIAN RAMIREZ
  • MEMBER
  • 5 POSTS
  • 2006 CHEVROLET HHR
  • 2.0L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 198,000 MILES
Temperature gauge stops working and AC will not work, but the car is not overheating. Check engine light comes on. I already replaced temperature sensor. Don’t know how to fix it.
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Sunday, September 27th, 2020 AT 12:14 PM (Merged)
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Hi Adrian,

I just need to clarify what you are saying. You said the temperature gauge stops working. Are you referring to the engine temperature (coolant temp) or the outside or ambient temperature is not working.

I am providing material based on the second (ambient temp) is not working because this would be related to the AC not working at the same time. The HVAC module uses ambient or the outside air temp to determine AC operation. Again, I am assuming when you say the AC does not work, you mean it is blowing hot air. If this is all true, then when the ambient temp sensor is not working it defaults to -40 degrees. So if the HVAC module thinks it is -40 outside then it is not going to allow your AC to blow cold air. Since you already replaced the temperature sensor, then it could be wiring or the cluster, or even the HVAC module.

You said the check engine light is on so before we go much further I would suggest you have the diagnostic trouble codes pulled and reply to this message with those. Because based on those, this entire post could be correct or way off.

Let me know when you get the DTCs pulled and what they are and we will go from there. Thanks

Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.

Kenny
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Sunday, September 27th, 2020 AT 12:14 PM (Merged)
Tiny
ADRIAN RAMIREZ
  • MEMBER
  • 5 POSTS
Hello Kenny, it is the engine temperature gauge will not work and when that happens the AC will not work either as soon as they reset the code everything works properly for a day or two and then it will happen all over again. I will try to get the code for you in the morning. Going to add a few pictures temperature gauge is on the left side.
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Sunday, September 27th, 2020 AT 12:14 PM (Merged)
Tiny
ADRIAN RAMIREZ
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Here’s a clearer picture. The car is on engine temperature gauge will not work and when that happens the AC will not work as well.
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Sunday, September 27th, 2020 AT 12:14 PM (Merged)
Tiny
KASEKENNY
  • MECHANIC
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Okay. I see the check engine light is on. Do you know what the DTCs are when this happens? I see you said you would try to pull that so hopefully that will shed some light on this.

Also, when you say the AC does not work, what actually happens? Does it just blow warm air or does it not do anything when you turn on the HVAC system? Or does it not even allow you to turn it on?

It looks like the temp gauge that is not working only has the PCM related to the HVAC system. The PCM sends the engine temp to the cluster via a message data bus which means the cluster is just displaying what it is told to by the PCM. The PCM also can disable the HVAC if needed so I am starting to think the PCM is the common thing here.

I just want to make sure we have a little more to go on before you replace a module like that because they are not the cheapest thing. Let me know what codes you find and we can go from there. Thanks
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Sunday, September 27th, 2020 AT 12:14 PM (Merged)
Tiny
ADRIAN RAMIREZ
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Okay, let me check with the mechanic to get the codes and also the AC only blows air.
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Sunday, September 27th, 2020 AT 12:14 PM (Merged)
Tiny
KASEKENNY
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Thanks. I think the DTCs will shed some much needed light on this for us. It is possible that the PCM is shutting down the compressor when the temperature gauge drops as a protection response because if it doesn't get an engine temperature feed, the compressor may add a load to the engine that will cause an overheat. Again, any codes should point us in the right direction.
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Sunday, September 27th, 2020 AT 12:14 PM (Merged)
Tiny
ADRIAN RAMIREZ
  • MEMBER
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Good morning Kasekenny. The code that it’s giving us is P0128 and it’s also saying that it’s -40°. Don’t know where you’re located but we live and Southern California it’s not -40° The engine temperature gauge was working for about a day and the air condition will not not work when the engine temperature gauge does not work only blows air. We already replaced the ambient sensor and also the engine temperature gauge and the thermostat. It’s also saying something about the intake sensor do not know if that’s related. If you have any answers greatly appreciate it.

Thank you Adrian
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Sunday, September 27th, 2020 AT 12:14 PM (Merged)
Tiny
KASEKENNY
  • MECHANIC
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Okay. That confirms basically what I was saying. The -40 is a default when the temp sensor/wiring/ECM has an issue with the engine coolant temperature sensor circuit. This DTC is saying the engine coolant temperature sensor (ECT) has a circuit issue. Basically, they are saying the same thing. If you already replaced the engine coolant temp sensor, then your issue is either wiring or an ECM.

I attached the test for this DTC. Let's fix this and I bet the AC not working will be fixed as well since I think that is the ECM shutting down the compressor because if it is truly -40 then the compressor will be damaged if it turns on. Check out the diagrams (Below). Please let us know what you find.
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Sunday, September 27th, 2020 AT 12:14 PM (Merged)

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