I recently bought a 1999 Cherokee 4.0 auto and the previous owner had one of those eBay performance chips spliced into the two wires going to the temp sender on the thermostat housing. I took it off because I didn't want it to mess the engine up but it seems it's alrdy done the damage.. I took the thing off and fixed the wires going to the sender. I noticed that the temp gauge is now
Going wild and will randomly go From far left too far right and vice versa. I am only getting one code P0117 low input signal or voltage I forgot which it is. So I replaced the sender and it didn't fix the problem. The actual temp of the engine seems
To be good hasn't actually overheated yet so I think it's just an electrical problem. I am just trying to figure it out and try anything else I can before I replace the ECM because I have a bad feeling that the "performance chip" fried the ECM as far as how the temp gauge
Works. On a side note I did notice the electric fan does turn on an off randomly when the jeeps just started up cold not sure if that's normal dice it's my first jeep. Thanks for any help! Nick

 

here is a wiring diag for the temp sensor


With the sensor unplugged check for 5v on the tn/blk wire, as far as the cooling fan cycling, make sure a/c is off, htr not on defrost. It will cycle with a/c and defrost....more rapidly if freon charge is low.
Good luck!

 

Ok cool I'll try that tomarow! And as for the fan cycling u gotta be right cause I have had the defrost on for heat.
I'll post results in the am

 

not getting even close to 5v at the tan/blk wire.

 

hers two quick videos i took of the gauge and how it acts... this is all at 55mph on the highway this morning.

 

Bump has anyone ever had this happen before to them? I'm gunna try another temp sendor tomarow

 

I know this and old thread but did you get it fixed? Mine is going to 210 then goes back down to the notch right above 100