Coolant Temp. Sensor

OK all you sensor guys who know what voltage is supposed to be supplied to each sensor I need help... I'm try'n to figure out if the sensor (coolant temp in T. stat housing) is bad or the wires going into it. Is there any way to trouble shoot it & how much voltage is there supposed to be at the plug/connector?
Any thoughts are truly appreciated.... OH ! 96 I-6 with an AW-4
Thanks !
Curt (aka Xtreme XJ)

With no one responding....

I'd dig through your FSM wiring for that info. Not sure what system it uses. Not even sure if uses a separate sending unit from the sensor the computer uses. If is the computer sensor, those voltages are always 5v. Be careful when testing computer-connected circuits and use a high impedance DVOM and do not short out things. Don't want computer problems!!

Judd:
Thanks for the reply... I wasn't sure if it was the wires or the sensor.... when I was testing it all I could get was 5v. This is a computer sensor (I think ) cause it lets the comuter know the coolant temp. At least your 5v comment is reassuring cause I was wondering if I was going at it right....I'm SO ignorant when it comes to wiring..and other things. If the "check engine" light stays on do I just discon. the batt. for afew mins. ?
Thanks again for the reply....
Curt (aka Xtreme XJ)

The sensor is the one located on the rear of the head on the drivers side....right?? Just making sure you are working on the right one. There are more than one. One is used for the guages and one is used to control the radiator fan. If your guage is reading something in the middle, just pull the connector on the sensor. The guage should read something different. On all the earlier guages, the sensor is a variable resistor to ground. I will see if I can find the resistances at each temperature. If I remember right it should be well under 300 ohms a normal temp.

Tom Houston
Loveland, Colorado

Xtreme....

Your XJ is OBD II since is a '96. Many of the later OBD II's will not clear codes with batt disconnection. Can only be done with a scanner. Your's being early, might still work. Be ever so careful with sensor/computer wiring. Is very sensitive to sorts and even many times to static charges!! The PCM, Powertrain Control Module controls everything on these later XJ's, from door locks to fuel injection to alternator charging rate. Treat it with tender loving care...or you will be replacing it!!

Judd & Tom:
Thanks for all the help... The sensor I'm talking about is on the T, stat housing....2 years ago (almost to the week) I was having simular problems & it was this sensor, knowing my luck it's about time for it to go out... Judd I believe mines a late 96.... I did discon. the batt. & after 24 hours so far no "check engine" light.
I'll keep my eyes, toes & whatever else I can crossed to see if this was the true problem. I did do a 200 mile trip today... no problems.....
Thanks again guys for the insight & thoughts....
Curt (aka Xtreme XJ)

2 cents

I believe the PCM sends a +5V dc signal to the sensor and then
reads the return voltage to measure temperature at the sensor
head. If it's like my Ford, it scales the temperature from +5V
(cold) to about 0.5V (for max hot temp). If you're reading +5V all
the time (even when hot) then I would think it's the sensor - if
the voltage (when hot) is substantially lower then +5V then
maybe the PCM is acting up, or the connection is intermittent.

Judd's correct about static charge - you may want to use a wrist
strap grounded to chassis before you probe any points
connected to the PCM.

If you solved it with a battery dis-connect - that's pure magic !!!

Good luck.

Rags told us many months ago that the newer OBD like on my 98 take 5 'cycles' to clear a fixed problem. A cycle being 'cold start, warmup, back to cold again' Had a check engine light on my 98 while going down a steep 3+ mile grade and I just coasted. Was all set to shotgun it with plugs, cap, rotor, wires, 2 O2 sensors. Did the 5 cycle thing he suggested and it cleared. Had it happen twice more on the same hill, now I down shift and play with the gas on it a bit.

Hey all:
I replaced the sensor and the check engine light was still on. Thats why I brought up the discon. of the batt. I HOPE!!! this works. I did have my mechanic put it on the scanner..... he said it's either the sensor or the wires going to it. So I went & got the sensor and installed it.
Again guys thanks for all the help.....
Curt (aka Xtreme XJ)