A/C Off Due to High Engine Temp

[Beaukz28]

This is a common problem I see on many GM's. it is caused by a mismatch in temp readings between the ambient, intake, and or coolant temp readings. This can be due to a t-stat not working correctly, One of those sensors being out of range, the connector to the sensor, wiring from the sensor to the ECM or the ECM itself. I have seen them all! I was told by engineering that the ECM is set up too sensitive for this code. I bet there will be a reflash eventually. One car took 4 ambient temp sensors until we resolved the problem. All four sensors varied by as much as 8 degrees due to tolerance.

[Cruzer1]

Originally Posted by tadams72

The quick way to reset the sensor is to shut the car down and disconnect the ECM Harness by the fuse box under the hood (front engine compartment, passenger side). I still don't know the cause of this but have had it several times myself.

You guys are great! I had the same problem yesterday. I received a message that my AC was shut down because the engine temperature was high. I also notice the temperature gauge was not working. I disconnected the ECM harness, reconnected and everything is working again.

[Blue70SS]

Originally Posted by Cruzer1

You guys are great! I had the same problem yesterday. I received a message that my AC was shut down because the engine temperature was high. I also notice the temperature gauge was not working. I disconnected the ECM harness, reconnected and everything is working again.

I have not tried the ECM harness disconnect/reconnect procedure, but my scenario throws up more questions:

Mine happened right after pulling out of an area making a right and doing a very quick 1/2 second throttle burst - the car was instantly turned 90 degrees, so I believe it may have happened due to being jarred. Now the check engine light comes on with "AC shut off due to high engine temp". I check the dash engine temp and it displays "--- " for temp, center console SS gauges show good oil pressure, but no oil temp (since we don't have real oil temp sensors - it's a derived #, I believe coolant temp must be in the equation).

Now here's the odd thing..... I have Aeroforce dual pod gauges off the OBD2 port. I changed one of the 4 readouts to Engine Coolant Temp and it is working. If I unplug the sensor on the drivers side head, the Aeroforce gauge readout no longer reads out correct (some gigantic #), I plug it back in and the gauge works again - but the dash reading still reads "---". This tells me the sensor is working.

To add to the mix, 6 months ago my gas level gauge turned off on the way back from Sturgis, but could be reactivated by doing a quick Wide-open-throttle pass. Fuel pressure readings were always good - so wasn't overly concerned, except it's nice to know when you need fuel when traveling LOL. It came back about 3 more times, but each time could be rectified by a WOT pass. Went away and never happened again.

I'll post up here when I find the solution. Brian at WyoSpeed suggested check the ECM wiring also.

[Blue70SS]

Well..... I tried disconnecting both of the ECM harnesses for a few minutes and reconnecting. It worked! Dash shows 54 degrees and Aeroforce gauge shows 53.5 off the OBD2 port (dash probably rounds up).

I suppose it could still be a bad sensor or loose wiring since it appeared with movement. Possibly the ECM has to be reset if it sees something wrong, where the OBD2 output still reads correctly? I didn't see or read any codes with a scanner - maybe if it happens again I'll do that 1st.

Next test will be having someone watch my gauges as I move the wiring on the ECT sensor, then on the ECM harnesses to see if the problem can be repeated.

If nothing there, I may test the dash connections.

[Blue70SS]

Originally Posted by tadams72

The quick way to reset the sensor is to shut the car down and disconnect the ECM Harness by the fuse box under the hood (front engine compartment, passenger side). I still don't know the cause of this but have had it several times myself.

Has it happened anymore? Is it possible that it comes back after some type of vibration/sudden movement?

[Blue70SS]

Originally Posted by danielblack60

It is untelling how many times I've had this customer concern. Every time I scanned one, the code was p0128. Engine coolant temp below threshold. Replaced thermostat and it was like it never happened

Not saying you all are having different troubles, but 98.3456 times out of 100 a thermostat will fix your problem.

PS: winter months are usually when you see thermostats start to fail, just food for thought.

I presume you mean "engine coolant sensor" and not the actual thermostat? The thermostat makes no sense, since the temp hasn't been reported as actually being high... just the message that implies it. My coolant temp via OBD2 was about 163 on a 160 thermostat. Thermostat does make sense if it really IS overheating though.

[Dznts]

Had this happen, seems to be a common glitch. I just shut the car off and pulled the ECM plug, and that fixed it. No problems since.

[Blue70SS]

Originally Posted by Dznts

Had this happen, seems to be a common glitch. I just shut the car off and pulled the ECM plug, and that fixed it. No problems since.

Wyospeed suggested it may be low pin tension on the ECU harness female pin. Still going to check for loose connections on mine too.

How long ago did yours happen?

[danielblack60]

Originally Posted by Blue70SS

I presume you mean "engine coolant sensor" and not the actual thermostat? The thermostat makes no sense, since the temp hasn't been reported as actually being high... just the message that implies it. My coolant temp via OBD2 was about 163 on a 160 thermostat. Thermostat does make sense if it really IS overheating though.

Sorry to leave you guys hanging. I haven't been on here in a while.

A dtc p0128 usually sets with the "a/c off due to high engine temp" message. The dash lies to you and tells you your car is running too hot, when in reality p0128 is a code for the car not reaching operating temperature fast enough. Which 99% of the time is caused by a stuck upen thermostat.

The actual description for dtc p0128 is "engine coolant temperature below thermostat regulated temperature". The reason the dtc is there is because the car needs to reach operating temperature as soon as possible in order to achieve closed loop and operate more efficiently.

If you have a 160 degree thermostat in your vehicle that is a good reason for that particular code to set. Your ECM is looking for coolant temps 180-210ish depending on ambient air temperatures, and if it stays around 160, or takes a really long time to reach 180ish, p0128 will set and your dash will tell you the car is running hot so you will take it in and get the problem fixed.

[PnCRedJwl2SS]

Same problem here...A/C Off Due To High Engine Temp in DIC. Would love to know how to disconnect/reconnect the ECM harness. Not even sure where it is...little help?

[Luckymex_dallas]

After three generations of camaro owners I think I may trade mine in and go to ford or Toyota. This and all the problemsI've had is senseless

[xqwzit]

I had the same issue happen yesterday. A/C off due to high temp message.... I didn't get the P0128 code. But I did have P0116, P0650, P1133, P1153. Coolant temp gauge on dash wasn't working and either was the oil temp gauge in the console 4pk gauges. All other gauges were working, I didn't unplug anything. I let is sit over night and everything worked fine this morning. Still trying to find out what the last two codes I got are. Hopefully figure this out so I don't have it happen again.

Now I do have a 160* t-stat, as required by the whipple supercharger. However I've had that on for the last 30k miles without issue.

[Brett64D]

I am now having this issue as well. Can someone post a pic of where to disconnect the ECM harness? Thanks!

[SandmanSS]

just finished installing headers last night; dropped it back down, reconnected battery and started right up with this message. thinking maybe coolant sensor was pinched near headers? also will look at the ECM idea. Anything else new come up?