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Is this an electric fan MOD

ChipsXJ

NAXJA Forum User
Location
Broken Arrow, OK
Is this an electric fan MOD to make the fan run constantly?


The electric fan comes on when the ignition key is turned on and runs constantly until the ignition key is turned off.


I think I verified that this added relay is a bypass for the electric fan.
When the added relay is disconnected the electric fan does not come on.
When the relay in the PDC is removed the electric fan des not come on.
We have replaced the sensor in the thermostat.
I have replaced the relay in the PDC.


Since it does work with the added relay....does that mean it is the ECM and it needs to be replaced?


When the AC or defroster is turned on the electric fan should come on, right?
2001 XJ.
 
they connected it into the PDC somewhere.....I have not pulled the PDC to see where....but I am thinking it is tied into the wiring for the relay in the PDC.
2 wires come off the PDC and connect to 2 terminals on the added relay and another wire from the relay to ground. I don't appear to be able to add pics to my posts.
 
Thanks - I will disconnect the 'extra' relay and see if the fan comes on at temp.

IF, the fan does not come on at temperature....is there anything else I can look at it or is it
most likely the PCM//ECU at this point?
 
the pcm will earth the control circuit of the relay whenever it wants to turn on the AUX fan.
it should come on around 104*C and also when the AC clutch is engaged, during normal operation.
If the coolant sensor is disconnected (or the circuit is bad) the AUx fan should run constantly whenever the engine is up and running.
to wire in a manual switch, a relay often integrated into the power circuit of the original wiring, as opposed to switching the control circuit that the pcm uses as it will cause a MIL light on OBD2 xj's. OBD1 will log a code but not switch the light.

good luck with it.
 
@Rainman - What I am hearing you say is that it is probably the coolant sensor (the one in the thermostat housing) circuit that is bad?
I have replaced the sensor already.....so it would be the wiring between the sensor and the ecm that would be suspect?

Thank you all for your replies.
 
If that was the case it should be storing a code.



god knows what bubba has done to that jeep.
if the fan is comming on and off with the ignition switch, thats not the PCM beeing upset with the coolant sensor. if that were the case the pcm would switch on the fan AFTER the engine cranked, fired and was running.
 
If that was the case it should be storing a code.



god knows what bubba has done to that jeep.
if the fan is comming on and off with the ignition switch, thats not the PCM beeing upset with the coolant sensor. if that were the case the pcm would switch on the fan AFTER the engine cranked, fired and was running.
 
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