I have a 97 RS 3.8. Recently my service engine light came on and the engine started to idle over 1000 RPM. I scanned the PCM and found error codes P0118-engine coolant temp sensor high input and P1635-PCM 5 volt reference circuit error. According to my scanner the coolant temp sensor wasreading a constant -38F. I replaced the sensor and cleared the codes. Engine starts and runs fine but the cooling fans do not turn on. Scanner reads about 160F when driving on open highway with about 60F outdoor temp but in stop and go traffic will climb to 220F.
I have checked the resistance on the new sensor and it is in range across 2 of the 3 terminals. The third terminal indicates open between the other 2 and to ground. On the old sensor I read resistance between all 3 terminals but reading is out of range since sensor is bad.
I have checked fans and relays and all are good. Any ideas other than replacing the PCM???

 

SLP Performance parts makes electric fan control switches that allow you to turn your fans on whenever you want and still retain factory operation! You can get them at alot of places (Summitracing.com) for example has them for about $73.00. I'm having the same problem with my car and I think this is a pretty good way to go.

 

What you have is normal operation. The fans are set to come on between 220 & 225.

 

Thanks z28pete and 96ss1557.
I was able to cross paths with my neighbor who is a Goodwrench mechanic. He said the same thing that the fans turn on at about 228F.
I understand that the temp gauge is really just an "indicator" but after getting in some stop and go traffic it went up to about 250F and caused the "check guages" light to come on until I could get on to the road again.
I have also checked to see that the cooling fans turn on with the AC and they do.
I think I will pull the coolant temp sensor out and verify resistance at the boiling point. Something isn't right when the guage tells me its overheating and the scanner says it isn't time for the fans to turn on yet.