Made a mistake and posted in modified section so repost here.


Driving down the road today and the check engine light comes on and I notice my temp gage is at zero, pull over have a look, engine doesn't seem hot do I continue driving and temp gage starts working again.


99 Cherokee, sending unit on thermostat, is it time to replace or could this be something else?

 

It could be a defectve engine coolant temp sensor or a broken wire at the ECT sensor connector.

Check the wiring at the connector and where it enters the fuel injector wiring manifold.

And/or, have a helper sit in the drivers seat while the engine is running. You wiggle the ECT wiring (and wiring at the firewall) and see if the temp gauge jumps around.

Edit: Generally, if the PCM sees and open or short in the ECT circuit it will illuminate the "Check Engine" lamp, like you see, and stores a code. If you can't find an apprarent wire problem, you will need to have the code read at an auto parts store and post the code number here for futher diagnostics.

 

OBD Scanner shows only one code P0118 Coolant Temp Sensor so I bought a sensor and will install tomorrow when engine is cool.


Today when I started the sensor was not working and then after driving about 5 moles the engine turned off so pulled off road waited a few minutes and it started and sensor also started working.


Any suggestions other then my plan to change sensor?

 

I think I may have found the cause. As I was checking the connection to the sensor I noticed the two wire coatings had worn then exposing the wires and allowing them to make contact.


Wrapped everything up to protect and prevent them making contact and will wait and see if I have a reoccurrence.