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Topic: Temp sensor for 1994 XJ

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Temp sensor for 1994 XJ

Can any one advise how best to test the coolant tempature sensor ( the one in the thermostat housing). I am not sure that my aux electric fan comes on when the temp reaches a critical level and with an Australian summer on its way, I would like to get it right asap. I can read the schematics ok, but when the leads go into and out of the PCM without knowing what goes on in there, I am lost. I can test the resistance of my current sensor at operating temp and it shows 1170 ohms (19.6k ohms when cold).

My Jeep is a 1994 Cherokee Limited RHD 4.0L and the electricals in the Grand Rapids FSM has a special listing for the RHD vehicle. The Temp guage in the dash comes from a separate sensor.

The fan does come on ok when I switch on the air con.

I would appreciate any advice

Regards from Down Under

Ingin



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Ingin
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Check the Tech section, if you do not have the service manual for your vehicle. http://www.greatlakesxj.com/tech/94fsm.zip I believe section 7 is the cooling system. With the 4L you should also have a vicous mechanical fan and the aux. electric fan. The electric fan has a relay that is in the Power Distribution Center (PDC). You should get a DTC of 35, if there is a problem with this circuit. Section 14 covers the Coolant Temp. Sensor.
This is directly from the manual ....
"The electric radiator cooling fan used in XJ models
(equipped with 4.0L engine, heavy duty cooling
and/or air conditioning) is controlled by the powertrain
control module (PCM) through radiator fan relay.
The relay is energized when coolant temperature
is above 103°C (217°F). It will then de-energize when
coolant temperature drops to 98°C (208°F). Refer to
Group 7, Cooling Systems for more information."
Here is the test for the sensor :
"Disconnect wire harness connector from engine
coolant temperature sensor (Fig. 34).
Test the resistance of the sensor with a high input
impedance (digital) volt-ohmmeter. The resistance
should be less than 1000 ohms with the engine at its
correct operating temperature. Refer to the Coolant
Temperature Sensor/Manifold Air Temperature Sensor
resistance chart. Replace the sensor if it is not
within the range of resistance specified in the chart.
Test continuity of the wire harness. Do this between
the Powertrain Control Module (PCM) wire
harness connector terminal-2 and the sensor connector
terminal. Also test continuity of wire harness terminal-
4 to the sensor connector terminal. Repair the
wire harness if an open circuit is indicated."

Hope this helps !

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Steve Martinek
SW Michigan.

2000 XJ Sport 
2005 F350 6.0L Crew Cab
1983 CJ8 - frame off in (slow) progress
1967 Mustang Fastback - future project - waiting for CJ8 to get done

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For the Resistance Chart noted above go to page 14-43 in the noted manual.

Couldn't paste the graphic in here easily.


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Steve Martinek
SW Michigan.

2000 XJ Sport 
2005 F350 6.0L Crew Cab
1983 CJ8 - frame off in (slow) progress
1967 Mustang Fastback - future project - waiting for CJ8 to get done

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Thanks Steve, great information and much appreciated. I will start down the track of replacing the temp sensor as mine reads above 1000 ohms at operating temp.

Thanks again for your help

Regards Ian

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Ingin
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Hi Steve, after quite a bit of wandering, I found the pages I needed thank you. Not easy for newbies to find, but well worth the effort. The details are exactly what I needed and if it was not for your guidance, I would never have thought to go to the "Fuel" section to look for coolant temperature sensors, so thanks again, I really apperciate your help.

Now for the enjoyable bit, testing and fixing.

 

Kind regards   Ian



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Ingin
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Hi Steve, Is the "black box" PCM a mystery box or does someone have schematics for what goes on in there. Connections in and out depend on what transipres inbetween and it would be nice to see that if possible.

Any help would be appreciated.

Regards Ian

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Ingin
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Ingin, from what I recall the wiring diagram only shows pin outs for the various "boxes". You might be able to find a actual schematic if you do a online search. You never know. I've never had a need to get that technical in fixing electrical issues. You are apparently interested more in the electronics of the PCM, which would be beyond my scope. I'm pretty reasonable with electrical issues but electronics was never my "cup of tea". You can verify this in Section 8W, which has the wiring diagrams.
Just trying to help a fellow "Limey" !biggrin  Only in respect to having been born there.



-- Edited by slvmart on Wednesday 12th of October 2011 07:44:40 PM

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Steve Martinek
SW Michigan.

2000 XJ Sport 
2005 F350 6.0L Crew Cab
1983 CJ8 - frame off in (slow) progress
1967 Mustang Fastback - future project - waiting for CJ8 to get done

Guest
Status: Offline
Posts: 9
Date:
Thanks Steve, you are right. I worked as a tech for Burroughs Corp, later Unisys, so this is right in my old field. I will do a google search, never really know what will come up. You have been a great help.
I see you are from SW Michigan, we lived in Detroit (actually house was in City of Troy) and I worked in downtown Detroit between 1981 to 1986 and just enjoyed it so much. Later I spent alot of time at Bluebell in PA where the new HQ were located in the old Sperry plant.
I have only had the Jeep for 6 months and loving it. It is my first 4x4.
My other "time consumer" is restoration of MG cars. Currently I have a 1971 B (Californian body, mine was rusted out too badly to restore) and a 1954 TF, now completed. Keeps me busy. I see you too have a string of vehicles to keep you busy.
Nice conversing with you.

Best regards Ian

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Ingin
 
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