View Full Version : Where does electric fan probe wire to?

ay ay ron
November 3rd, 2017, 10:13
Stupid question, but Im driving myself crazy trying to find an answer in the search and in other locations.

91 xj. My temperature probe that plugs into the radiator has been cut off by my clutch fan. I thought this was plugged directly into the electric fan somewhere, but I picked up another used e-fan, and it didnt have the radiator probe either.

I think im missing something here. Where does the fan control temp probe wire up to? Any pics or comments would be helpful.


November 3rd, 2017, 12:38
your 91 should also have a temperature sensor on the thermostat housing. for i believe just the gauge. then there is one on the drivers side block for the PCM. and your E Fan may be controlled by just the PCM.

From 94 FSM

When coolant temperature is above 88C (190F),
the powertrain control module (PCM) grounds the relay.
Battery voltage is then applied to the fan through the relay.
When coolant temperature is below
88C (190F), the PCM opens the ground path to
the relay. This will prevent the cooling fan from being
Whenever the air conditioning is used, the PCM
engages the auxiliary cooling fan. It provides a
ground path to the cooling fan relay.

November 3rd, 2017, 19:05
Older XJs had a probe / fan switch in the radiator but no such thing on the 91. There is a coolant temperature sensor in the thermostat housing at the front of the head and a gauge sender at the back of the head on the drivers side (and those were combined in 97). The electric fan is controlled by the computer whenever (a) the AC compressor is engaged, or (b) when the temperature at the coolant sensor in the thermostat housing hits ~220 (give or take, changed every year). The coolant sensor is also used to control air-fuel mix and some other things.

ay ay ron
November 4th, 2017, 12:03
Hmm, I'm dumbfounded then haha. All I know is that my Efan used to work, and then it stopped working. I went to investigate and found that the probe in the radiator was cut off. So let's just assume I have an older style that used the probe in the radiator for whatever function, where does that probe connect to? Not the probe end, that obviously goes into the radiator, but where does the wire run to? I don't see any cut wires anywhere.

November 4th, 2017, 12:35
Are we talking about the thermal switch in the lower left (near the output) of the radiator?

ay ay ron
November 4th, 2017, 15:26
Its this probe. It was plugged into my radiator. Trying to find out where the other end goes. It got cut off by the clutch fan.


November 4th, 2017, 15:33
I don't think that is something that was OEM.

ay ay ron
November 4th, 2017, 15:38
I don't think that is something that was OEM.

That would explain my struggles haha. Anyone want to confirm this?

Previous owner had a lot of stuff wired up. Oh man, Im going to have a hell of a time trying to figure this problem out. It seems my fan will not work without it plugged in, so they must have wired up some custom regulator.

November 4th, 2017, 19:48
Its not stock

ay ay ron
November 4th, 2017, 22:32
Thanks everyone