Aux fan will not engage when supposed to

[Ecomike]

Well I found some data on the 1997 temperature sensor in the thermostat housing.

11, 370 to 13,600 ohms at 68 F (they list a min/max acceptable value!)
1630 to 1870 ohms at 158 F
640 to 720 ohms at 212 F

The air temperature sensor in the intake manifold hase the same values.

So now the question I have is why does the fan come on when you disconnect the temperature sensor? Perhaps the computer recognizes the sensor is disconected and by default turns on the fan as a failsafe step?

I am still loking for data on the sensor at the rear on top of the engine valve body.

My think is that since pulling the connection to the sensor at the thermostat housing turns on the elctric fan, it must be the sensor that the computer uses to decide when to turn on the electric fan.

It looks like the 97 manual (I am not sure is this beast over 1700 bloddy pages it):banghead:shows only that one sensor running the gauge, fan and giving the PCM data it needs to calculate the A?F ratio, and the 96 was the model year that changed, 96's are suppose to be like 97s. Is that the OEM engine in that 96 jeep? Is it an older head perhaps? Just out of curiousity why not pull the connector to the rear sensor and see what the gauge does, and then do the same on the front sensor and see what the gauge does.

The 97 fsm does say the fan is turned on by the PCM through a relay at
217 F, and turns off at 208 F.

 

[Blaine B.]

The sensor in the thermostat housing is for the PCM to regulate fuel mixture based on coo lant temp, as well as to kick on the eFan...

Unless it's a renix. That has 3 sensors. One on the top of the block for the gauge, one on the bottom side of the b lock for PCM, and then another in the radiator for eFan.

Then I think in 97 or 98 they converted to strict ly one sensor in the thermostat housing which contro ls fue l mixture, eFan, and the gauge.

 

[Ecomike]

The sensor in the thermostat housing is for the PCM to regulate fuel mixture based on coolant temp, as well as to kick on the eFan...

Unless it's a renix. That has 3 sensors. One on the top of the block for the gauge, one on the bottom side of the b lock for PCM, and then another in the radiator for eFan.

Then I think in 97 or 98 they converted to strictly one sensor in the thermostat housing which controls fuel mixture, eFan, and the gauge.

He has a 96.

So there are some suptle differences between 96 and 97, contrary to most reports here?

I was trying to find him some data to use to verify that his guage sensor is accurately reporting the engine temperature because he does not have any way yet to determine which sensor is wrong, the gauge sensor or the PCM's temperature sensor.

 

[corbinafly]

96 was a transition year, so there were ongoing changes throughout the year. I have a 96-98 head on my stroker and it had the hole for the temp sensor on the rear of the head like the earlier models.
I'd do what 8mud suggested to see if the CTS is out or range compared to the IAT.

Kyung

 

[8Mud]

He has a 96.

So there are some suptle differences between 96 and 97, contrary to most reports here?

I was trying to find him some data to use to verify that his guage sensor is accurately reporting the engine temperature because he does not have any way yet to determine which sensor is wrong, the gauge sensor or the PCM's temperature sensor.

The changeover, at least for the export models, was mid 96. Some 96's seem to be mostly 95's, some half 95, 96 and others second half or full 96 maybe a bit 97. I've had to play musical connectors before, the front O2 on mine is a 96 the rear a 95 connector, mine is OBD 1. Among other anomalies.

My 96 looks like this at the PDC.

 

[8Mud]

The relay location is often found inside the lid for the PDC. I can't imagine your XJ doesn't have a fan relay someplace.
Maybe a mechanic pulled it to test in another relay location and forgot to reinstall it or left it laying on the air box and it fell out onto the street someplace.

 

[basso4735]

The relay location is often found inside the lid for the PDC. I can't imagine your XJ doesn't have a fan relay someplace.
Maybe a mechanic pulled it to test in another relay location and forgot to reinstall it or left it laying on the air box and it fell out onto the street someplace.

thing is, theres nothing in that slot for the relay. nothing it would plug into. its just an open slot.

and yes, its an oem 96 engine as far as i know.

i took some pics on the previous page if you guys didnt see.

 

[Ecomike]

It may be behind the dash near the other A/C controls. I recently took photos of about three relays around the A/C system, under the dash, planning to post them here and ask everyone what they are for? One of them may be what you are looking for. 3 of them were the standard relays and I think at least two of them were somehow tied into the A/C controls. I should add that mine is an 87 Renix, but that may be one area they left alone all the way through to 96.

Its not hard to pull the dash face off and see them, they are in plane view with the dash panel removed.

 

[8Mud]

thing is, theres nothing in that slot for the relay. nothing it would plug into. its just an open slot.

and yes, its an oem 96 engine as far as i know.

i took some pics on the previous page if you guys didn't see.

Maybe yours is some kind of bastard setup and the relay is in the old (Renix)location, near the front of the drivers side fender well near the top. Or the 94 (95?) location first (front) in the row down the passengers side of the PDC.
I have seen some differences in the PDC, my owners manual diagram and what is in my 96 XJ are different as are the late 96 varieties (I believe).
Hold your finger on a relay and have somebody plug and unplug the front sensor plug, repeat with all the relays. Or have them turn the AC on and off, if the fan is running a relay is closing someplace. The HVAC relay and the fan relay.
Get a schematic and follow the wire back form the PCM to the sensor or just swap out the front sensor and hope you get lucky.
I had a look at the wiring diagram, the PCM turns on the fan (relay) when the AC is turned on and when the sensor tells it to, over the same wires from the PDC to the fan relay, there is no splice or parallel circuit.
Seems likely that the sensor is faulty or maybe a bad connection causing high resistance in the wiring, fooling the PCM into thinking the system is cooler than it is.
You may just have a fluke and the fan relay was forgotten at the factory. But doubtful, the AC is tripping a relay someplace to turn the fan on, yes/no?

 

[basso4735]

haha im not that worried about it, the fan works with the a/c. ill just replace the temp sender and see how it goes.

 

[8Mud]

haha im not that worried about it, the fan works with the a/c. ill just replace the temp sender and see how it goes.

A Mil code 35 means there is something wrong with the fan relay circuit, a code 44 means it's the Eng. temp. sensor. But Mil codes are sometimes not there, unless the problem is serious. Sometimes Mil codes are stored but don't trigger a "Check Engine Light". Mil codes aren't definitive, but can get you pointed in the right direction. GoJeep has a pretty good (newer) list of codes.

 

[basso4735]

oh, my CEL didnt come on when i started it up this morning. well it did for a sec like its supposed to but it didnt stay on.