Thermostat may be stuck closed.

[rojoes]

Did you verify that there is current going to thermostat?

Check to make sure the connector is plugged into the thermostat securely.

 

[minitrucking02]

Check your pids, fuel trim. Closed loop, stuck open.

 

[gokaipyro]

I found out the problem with the no heat problem. My radiator cap had the part that seals the overflow tank broke off. So I bought a new cap and you can see the difference. So now I have heat and no coolant loss. But my thermostat code is still on.


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[JKimSonic]

Is it a plastic housing or metal housing thermostat unit? The plastic housing units are said to be more problematic as mine failed and had a slight leak. It could very likely still be under warranty anyway...Check with the dealer since the thermostat unit is around $100.000 let GM pay for it.


Symptoms of a P0599 code will vary depending on the position of the thermostat at the time of failure, however, it is unlikely that there will be any noticeable difference in the operation of the vehicle. The check engine light will illuminate and one of the above codes will be set The temperature gauge may read abnormally high if the thermostat failed in the partially closed position, conversely, it will read lower than normal if the thermostat failed in the full open position

Read more at: P0599 Thermostat Heater Control Circuit High Code
Copyright OBD-Codes.com

Where is this temperature gauge you speak of? My sonic doesn't have a temp gauge?

 

[RMinNJ]

Where is this temperature gauge you speak of? My sonic doesn't have a temp gauge?

We don't have a temperature gauge... There should be laws against selling a car without one
as it tells you something is wrong. I think GM relies on the check engine light for that but its not really the same thing..


Many of us brought the ultraguage for this because it tells us a bunch of other stuff also.

 

[Bchana916]

I'm still getting the code p0597 after I changed the thermostat.


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I received the same code after changing my thermostat, how’d you resolve your issues

 

[Dingleberry69]

Was there any corrosion on the electrical connector going to the thermostat heater, also on the housing, there is a secondary temp sensor, maybe that one’s gone. Check the connectors, if you see green, they will need a super good clean. Corrosion (Aka green death) is not electrically conductive, so the ECU is not getting the signal. Also check the wires themselves between the ECU and the thermostat, with a multimeter. There might be a break in the wire, therefore no continuity. Might also be an issue with the ECU, however I have been told that is incredibly rare. Also, did you replace with an original GM thermostat or Delco, or did you go aftermarket? For QC reasons, longevity reasons, on a relatively critical component, I would only do Delco or genuine GM. Might be possible that you installed a defective part, and the heater was dead from the get go. Also the original housings are made of plastic, if it’s still the original unit, it may be very prone to cracking. I faced the same situation as you with the P0597 code, and I elected to go with the GM original thermostat and housing to replace, code disappeared immediately upon startup, with the bonus peace of mind that I won’t have to worry about cracking of the housing due to age and heat cycles. Replacing the housing is super easy, 2 electrical connectors, 1 hose on top that’s secured by a clip, 1 pipe, 3 hoses, and 4 bolts. 30-45 mins tops to replace with the same size e-torx bit you used to replace the thermostat E10 I thinks. Before you replace, disconnect the battery, so the ECU has time to reset while you replace the unit. Housing comes complete with both sensors as well.

sure it’s more expensive than a $30-40 aftermarket unit, but will almost certainly fix the problem.

 

[nutznboltz]

Was there any corrosion on the electrical connector going to the thermostat heater, also on the housing, there is a secondary temp sensor, maybe that one’s gone. Check the connectors, if you see green, they will need a super good clean. Corrosion (Aka green death) is not electrically conductive, so the ECU is not getting the signal. Also check the wires themselves between the ECU and the thermostat, with a multimeter. There might be a break in the wire, therefore no continuity. Might also be an issue with the ECU, however I have been told that is incredibly rare. Also, did you replace with an original GM thermostat or Delco, or did you go aftermarket? For QC reasons, longevity reasons, on a relatively critical component, I would only do Delco or genuine GM. Might be possible that you installed a defective part, and the heater was dead from the get go. Also the original housings are made of plastic, if it’s still the original unit, it may be very prone to cracking. I faced the same situation as you with the P0597 code, and I elected to go with the GM original thermostat and housing to replace, code disappeared immediately upon startup, with the bonus peace of mind that I won’t have to worry about cracking of the housing due to age and heat cycles. Replacing the housing is super easy, 2 electrical connectors, 1 hose on top that’s secured by a clip, 1 pipe, 3 hoses, and 4 bolts. 30-45 mins tops to replace with the same size e-torx bit you used to replace the thermostat E10 I thinks. Before you replace, disconnect the battery, so the ECU has time to reset while you replace the unit. Housing comes complete with both sensors as well.

sure it’s more expensive than a $30-40 aftermarket unit, but will almost certainly fix the problem.

How did you remove that little hose on top? It looks like one you squeeze to remove but I don't want to break it. Thanks in advance for your help! Ken

 

[Dingleberry69]

How did you remove that little hose on top? It looks like one you squeeze to remove but I don't want to break it. Thanks in advance for your help! Ken

There’s a clip on that pipe that pulls off. At first I was under the impression that you squeeze and pull, but then it came to me that I was going at it all wrong. Just about broke the clip myself. Just don’t lose the clip, which is real easy to do. I did and it was a fun search.

 

[nutznboltz]

There’s a clip on that pipe that pulls off. At first I was under the impression that you squeeze and pull, but then it came to me that I was going at it all wrong. Just about broke the clip myself. Just don’t lose the clip, which is real easy to do. I did and it was a fun search.

I got it right after posting this. Also damn near lost that clip. Luckily it fell on the ground instead of disappearing into the engine bay abyss. Sometimes we get lucky. Thanks for the reply!