I can get dash cluster, ecm, and bcm from donor suv. Would changing all 3 be enough to make computer system happy? Or are there other hidden computers?
The only way to know that is to try, unless you can test them. Make a plan to replace the most likely bad actor first and see if it works. If not, pick the second most likely problem part and check again. If they donāt fix it try the third. I suppose there is always a chance that one of the replacement parts doesnāt work right, but donāt worry about that until you see if on or more do or parts work.
Itās a little overboard to change all items. But everything I read about computers and programming gives me pause. Read that dash powers up and looks for ID. From where? The ecm? Or bcm?
I highly suggest you obtain the wiring diagram(s) that shows the coolant temperature sensor(s) in relationship to the pcm and cluster
And it would also be a good idea to obtain the factory information which describes what the pcm and cluster do when they see problems with the coolant temperature sensor(s)
I put that in parentheses because Iām not sure if you have more than 1 sensor . . . but I suspect itās only the one
Since you arenāt getting a reading on the temperature gauge it most likely means that the circuit to the sensor is either OPEN or SHORTED, depending on how the circuit is designed. If that same sensor is used by the ECU to check the engine temp then fixing that circuit should make things right again.
Got a better code reader at store. Says code 0118 ect circuit and 0128 ect too low? Said ect temp was 140f. Cleared codes, and ac works now. And temp gauge works. Idled for 10 min and temp went up to 165. Drove home and after 10 min the ac went off. And temp gauge went back to cold.
Sounds to me like a damaged wire or poor connection somewhere (possible internal to the PCM). The temperature sensors are thermistors which are extremely reliable.
Change plug. Check wire harness for nicks and scuffs. And pcm last? I donāt have schematic. Where does ect wire route too? Ecm is on top of battery. About 1ā from ect sensor. Ironic the route is so short.
Hereās a schematic showing the ECT sensor circuit (click for full size). I donāt recall if the year of the vehicle was ever mentioned. This schematic is for 2006 with the 3.4L engine, which should be similar to later years. If the engine is not the 3.4L, the diagram is a bit different.
Notice connector C150 between the sensor and PCM, which is also part of the MAP sensor circuit.
The PCM sends ECT related signals to the BCM through the high speed data lines. The BCM then relays the signal to the cluster through the class 2 data line. The cluster deciphers the signal to display on the gauge.
Since the problem came back again I suggest you inspect the wiring for an issue. You could even test the wiring using the diagram for reference. If you donāt find any signs of a wiring problem I suggest you replace the sensor. I think that is what is causing the problem.
Took out thermostat. It was stuck open.since scan tool said temp was 140f at store I kinda thought something was up. Replaced it and drove to AZ near me to read cel and it says 0405 egr circuit. There and back ac works fine. Drove to grocery store just now and ac still works. Why does a cold motor shutdown the temp gauge and give you overheat message though?
Replacing the thermostat to correct the problem you were having seems a little strange to me. Does the temperature gauge work correctly now? If it now works correctly then the trouble with it may have with the wiring to the ECT sensor. Depending on how the circuit is designed would determine how the gauge would react to the problem. If the circuit is designed to make the gauge show colder as the resistance goes lower then a short to ground on the line would make the gauge read cold even if the engine temp was high.
According to the factory service manual:
The engine coolant temperature gauge defaults to 0Ā° or below if:
ā¢ The ECM detects a malfunction in the engine coolant temperature sensor circuit.
ā¢ The IPC detects a loss of serial data communications with the BCM.
ā¢ The BCM detects a loss of serial data communications with the ECM.
coolant temperature sensors are NTC . . . negative temperature coefficient, I believe
sky high resistance = low temperature indicated
very low resistance = high temperature
Thus, higher resistance . . . or open circuit would mean a lower temperature indicated. As a matter of fact, I believe negative 140 degrees indicated is a classic case of open circuit
Short, by definition, I believe, is lower resistance . . . which would cause a higher than normal reading
I do agree with your belief that there is a wiring problem
The scan tool said temp was +140f with the open thermostat at store,
I cleared codes and everything worked. Till I drove home.
And found stuck open thermostat.
I disconnected battery and all is working now with new thermostat
Temp gauge did go 180 deg out of position 1 day. Now it seems to be back to normal.
Had abs light and stabilitrak message. RF sensor issue. Changed bearing and abs light is off. But I still have trak message. And tpms issue since 2 sensors are bad. Could tpms issue be root cause of trak issue? Temp overheat issue seems to be gone. Ac works fine.
Iām not an expert on the TPM system but I would definitely think that a problem with the wheel sensors could cause a tracking issue also.
Nah . . . 
I can drive it for 5 min or and I get no warnings. The tpms light is on dash but message center is quiet. Then all of a sudden the alarm sounds and the messages start their scroll. Service stabilitrak, service tire monitor system. I think there is 1 more warning but I ignore it. I did reset tpms so it sees 2 wheels. But next time I start car, those wheels register zero.