I recently acquired a 1989 C2500. The temperature gauge was not working, but when the car was started the gauge would work in test.

I decided to replace the Temp sensor next to the thermostat. After replacing it and the thermostat the gauge still did not work. While rechecking some stuff I noted a second sensor near the exhaust on the drivers side of the truck was disconnected. I reconnected it and the gauge started working again.

But then the Service engine soon light came on.

I shorted the 2 upper right pins of the diagnostic connector and got a code 14 "COOLANT TEMPERATURE SENSOR (CTS) CIRCUIT (HIGH TEMP)"

The gauge does not read high and appears to work normally. The new thermostat is working fine.

Is there a problem with the new sensor? the other Sensor? I'm going to try and clear the computer and see if it goes away.

 

The sensor down low if for the dash gauge, the one by the thermostat for the computer and associated with the code. You already changed that sensor - interesting to see if the code stays gone now.

 

Ok resetting the computer did not fix the issue. I took readings of both sensors with an ohm meter and got about 540 ohms with the truck warmed up. I decided to reconnect the one sender I replaced and the service engine soon light went out.

I took out the new sensor and put the old one back and the gauges still work AND the service engine soon light is out. So the problems was the new sensor.