[SnaFu]

This morning i got a "coolant sensor bad" message on the VIC. It is intermitent (sp). The first time it came on i got the message twice and then it went away. Since then i get it once and not again after restarting. Would i be correct in thinking that the sensor is on the top of the engine, where the radiator hose goes into the block? Truck runs fine and temp is right where it has always been. Coolant level is at full. i have read on this forum and others that it is in the resivoir (sorry my spelling sux) and that it is in the block. Does anyone know for sure where it is? Not getting a CEL.

BTW, Jeep is a '97 GC, with a 4.0 engine.

 

[CSMDakota]

The coolant temp sensor for the 4.0 L is located on the thermostat housing, (front top of the engine, just above the serpentine belt). It threads into the housing on the driver's side at an angle, and has a 2-pin connector on it.

Good luck

 

[SnaFu]

The coolant temp sensor for the 4.0 L is located on the thermostat housing, (front top of the engine, just above the serpentine belt). It threads into the housing on the driver's side at an angle, and has a 2-pin connector on it.

Good luck

Thanks Dakota, that was where i thought it was. Got a reply earlier on JU and was told on the WJ it is in the overflow tank. maybe it is there on the WJ. Who knows. who cares. lol, I have a ZJ.

 

[WJ Rockkrawler]

my buddy is havin this same problem with his 5.9 and we've replaced the tank sensor and the block sensor and the light still comes on intermitent...any sugestions ?

 

[CSMDakota]

I'd check out the coolant tmeperature sensor wiring.

Visually you can check for a pushed out pin or suspected weak point in the wiring, but it'd require a bit of luck to find something like that.

The best way to do this would be to unplug the temp sensor and the engine harness at the ECU, then run an Ohm meter across each of the two wires at each end, one at at time. Should get 0.00 Ohms, and that reading should be steady as you wiggle the engine wiring harness. I wish I knew which pins on the ECU end they were, I'm not sure if the factory service manual gives this info or not, I'll try looking tonight...

It could be something else, but this check is free and makes sure your ECU is getting a solid connection to the sensor.

 

[Lloyd]

On mine the "coolant sensor bad" was tripped by the level sensor on the overflow tank. I cleaned it and it worked fine for over a year. Now it's coming on occasionally.


Good Luck!

 

[SnaFu]

Thank you everyone for the help. It would appear that the only thing i can do is check both sensors.

 

[CSMDakota]

If you decide to check out the temp sensor wiring, here's some more info: Note this is from 1998 ZJ factory manual, should be ~same for 1997.

The PCM (under the hood, passenger side firewall) should have three, 32-way connectors on it; A, B and C. I don't know which is which, either they'll be labeled or you'll have to use process of elimination.

Connector A has two pins that would be of interest to you:
A4 = Sensor Ground (also ground for IAT sensor)
A16 = Engine Coolant Temperature Sensor Signal

1. Unplug the (-) side of the battery.
2. Unplug connector A
3. Unfold a small paperclip and stick it in A16
4. Unfold another small paperclip and stick it in the coolant temp sensor connector pin corresponding to the tan wire with the black tracer.
5. Put an Ohm-meter across each end at the paperclips and see if you get a solid 0 Ohms, even if you wiggle the harness at several spots.

Repeat 3. thru 5. for A4 and the coolant temp sensor connector pin corresponding to the black wire with light-blue tracer.

If you get O.L. or infinite resistance, or are able to make the continuity intermittant while wiggling, it is a wiring problem. If this turns out to be the case, we can move forward at that time.

Like I said, good chance it may be something else, but this is an easy check that is free.

Let us know how you turn out.

 

[heydave]

I unplugged my VIC. All my problems went away! :mrgreen:

 

[SnaFu]

Update

Unplugged the sensor on the front of the engine, where the raditor hose goes into the block. Cleaned the connections and reseated the connector. So far so good, but it has only been one day. got my fingers crossed. :lol: