Temp gauge not reading correctly

[tomchitwood]

Hello all, I need to pick your brains. I have a 1992 jeep Cherokee sport 4.0. I did a head gasket job on it and the temp gauge worked for about two days. It quit reading all together so I bought a brand new gauge temp sensor and it reads wide open all the time. I can unplug it and the gauge goes back down to zero but with it plugged up, even with the engine ice cold, it reads all the way to the right.?!? Bad (new) sensor? Thanks everybody, Tom

 

[greg92jeepxj]

Hey to ! Welcome to Jeepz.com ! I to own a '92 jeep XJ 4.0 H.O. . Had a look at the FSM just to verify if wiring goes to ground but that is not the case with our jeeps. The tan/bk wire feeds back to the PCM and the bk/ lb splices to the CPS. Suffice to say , the sensor would not be grounding so I believe you may have a bad CTS. Too bad you don't have another sensor lying around to swap in just to see if you get a more normal/acceptable reading to verify the new part is defective. Don't know if you did the ohm test to it , if it reads infinite(zero) , its bad . If the reading is the same warm engine or cold , confirmed , its bad. By what you posted , cold or warm engine , your getting the same reading. I would say a replacement is warranted.

 

[greg92jeepxj]

Hey again , got more research to do from the FSM , will research later today . There are more sensors . Will research soonest . Greg

 

[tomchitwood]

Thanks for the quick reply. The plug for the cts only has one wire so I figured it was the grounding type. I will try the ohm test and see what it says. I don't know why I did not think of that. Due to money issues and everybody else's vehicle needing fixed, this thing has been down for 6 months. I have it back on the road now after an engine swap, then new head gasket on new to me motor. I just have to get the temp gauge reading right so I can keep an eye on it.
Thanks, again, looking forward to seeing if you have any more ideas.
Tom

 

[greg92jeepxj]

Hey Tom , have included two pages from my FSM that I hope may help you as far as identifying sensor by wiring color code .
You mentioned you have a one wire sensor , I did not ask if the sensor you changed was in the thermostat housing or the cylinder head. The book also mentions coolant temp sensor in engine block but I don't think your engine has this as that was used with AMC but your engine was swapped in and I don't know what year it is . Hope this helps and I have the manual as a reference should you have any questions I will try to address them from the manual . Greg

 

[tomchitwood]

Greg,
It is the sensor on top of the head, in the back of the motor, right against the valve cover. I checked it yesterday with my voltage tester and it ohm'ed out at zero. It is showing a straight ground through the sending unit which should mean the sensor is bad. I took it out to exchange it, but broke it, so I'll just have to buy a new one and see how that works. Good thing they are only $8.00. Thanks for your help. Except for this little hiccup she is running great, better than ever.
Thanks again, Tom

 

[greg92jeepxj]

Your more than welcome Tom . I'm sure your jeep is running great after a cylinder head gasket job and the fact that you performed it and not some one who has to bang out multiple cars every day and can't give it the detail that you can . Not many mechanics will ever fix your jeep better than you under those circumstances but I respect professional mechanics who can and do . I seem to forget that a coolant temp SENSOR is different from a coolant temp SENDER as the sensor communicates with the PCM and the sender communicates with the dash gauge , in this case. Sorry for the confusion and am very happy all will be worked out soonest . I'm certain your dash gauge will not lie to you any more after this and you can drive it confidently knowing the true engine temperature. Feeling good that all is well . Ya gotta love a great running 4.0 H.O. ! Greg