Quoting transparentdsm:
in my experience this has been the most common issue:
CTS wiring harness. you'll have to trace the wires back and find where there corroded or broken.
^Yep. Your ECU isn't seeing coolant temperature. You need to figure out why.
From another thread with someone having the same issue:
Quoting GSTwithPSI:
You need a DVOM with long leads. I put my meter on the windshield of the car, and clamp one lead on the wire at the sensor connector. Then, I take the other lead and probe the ECU pin while looking at the meter through the windshield.
Coolant temp sensor wiring:
T-pin front: Coolant temp sensor (connector B02): Green/black (crossbar of T) and yellow/green (stem of T position)
First, clamp a meter lead on the Green/black (crossbar of T, or top part of the T) wire at the sensor.
Then, you need to find pin 20 at the ECU:
ECU Pinout. Put your meter lead there, and see if there is continuity between the ECU pin, and the sensor connector. If not, then your ECU is not getting a signal from you coolant temp sensor. And, I'd bet my life that it isn't getting one.
The other wire, yellow/green (stem of T position) goes to ground. It goes to the ECU sensors ground on pin 24. You can do the same thing for this circuit as you did for the other, or you could just ground it somewhere in the engine compartment. Eventually, you want to make sure it is properly grounded through the engine harness back to the ECU though.
If your car isn't seeing coolant temperature, it is screwing all kinds of sh*t up. You need to verify it is working. It would be best if you had a logger or something, that way you could hook it up and see exactly what the ECU is seeing...
Lastly, here is a link to the library where the coolant sensor wiring diagram is located.
click Look on page 148 (actual document page number, not the Adobe page number)
Threads:
click and
click
