Temperature Gauge Reading Engine overheated Idle Engine

[WITCH1975]

I have a 2008 Chevy Tahoe, purchased it about 2 months ago and trying fix all issues. However, this one has me stumped. I can be driving and the gauge will shoot over whichever way and say one of 2 things. Engine overheated Idle engine or Engine Hot turn off A/C. We have changed the Temperature sensor, the plug that plugs into the sensor, thermostat, the water pump, and the hoses. I haven't changed the Radiator yet or head gaskets. Has anyone else had this issue? If so, what did you do to fix it.

 

[Fless]

Strange that the gauge shows low temp but the message is for hot. Can you watch the PID for the engine coolant temp with a scanner to see what it's reporting as this happens? I bet the coolant temp sensor is still mis-reporting and the PCM reverts to "hot" as a default. Just a guess on my part.

What diagnostic trouble code (DTC) is active?

 

[mikez71]

+1 on checking a scanner for the temp..

Both wires go the ECM, I would think a bad connection should only swing one direction..
(Unless as Fless suggested it may default to hot when signal is bad)

A leaking head gasket shouldn't swing stone cold.
Another bad sensor with the exact same symptom seems unlikely.

I wonder if it could be a bad ECM or gauge cluster..
Might be worth checking/cleaning the pins on the ECM and check yellow wire..
(If yellow wire had a break, that occasionally contacts ground)

 

[WITCH1975]

Strange that the gauge shows low temp but the message is for hot. Can you watch the PID for the engine coolant temp with a scanner to see what it's reporting as this happens? I bet the coolant temp sensor is still mis-reporting and the PCM reverts to "hot" as a default. Just a guess on my part.

What diagnostic trouble code (DTC) is active?

So right now when it's been happening no code is showing. Before it was the coolant temp sensor, so we changed it and changed the plug to be on the safe side. P0117.

+1 on checking a scanner for the temp..

Both wires go the ECM, I would think a bad connection should only swing one direction..
(Unless as Fless suggested it may default to hot when signal is bad)

A leaking head gasket shouldn't swing stone cold.
Another bad sensor with the exact same symptom seems unlikely.

I wonder if it could be a bad ECM or gauge cluster..
Might be worth checking/cleaning the pins on the ECM and check yellow wire..
(If yellow wire had a break, that occasionally contacts ground)
View attachment 490410

So, I already changed the Cluster, so unless the vehicle it came out of had the same issue. I would lean towards a bad ECM or i seen some where a bad BCM. So, looks like I will be ordering another ECM.

 

[WITCH1975]

Strange that the gauge shows low temp but the message is for hot. Can you watch the PID for the engine coolant temp with a scanner to see what it's reporting as this happens? I bet the coolant temp sensor is still mis-reporting and the PCM reverts to "hot" as a default. Just a guess on my part.

What diagnostic trouble code (DTC) is active?

I am going to look up the scanner when i get home and drive it with connected to check what it says the live temp is. Cause as of right now it doesn't throw a code for it.

 

[WITCH1975]

Strange that the gauge shows low temp but the message is for hot. Can you watch the PID for the engine coolant temp with a scanner to see what it's reporting as this happens? I bet the coolant temp sensor is still mis-reporting and the PCM reverts to "hot" as a default. Just a guess on my part.

What diagnostic trouble code (DTC) is active?

P0117

 

[j91z28d1]

there's 2 intake air temp pids you can watch live too.(also ambient air temp) I've never been able to figure out what sensor it's using for one of them, as it seems to be a mix of coolant and air temp in the mass air sensor blended together. if your scanner shows normal coolent temp while the dash is showing over temp, check for air temp.

just a heads up, if you replace the ecm, you'll have to program it to the truck. I believe there's some work around for that with Dorman parts, but a used oem will definitely have to be flashed. I'm surprised the dash gauges didn't need flashed. did you change that out because of this issue? or before this started happening