Electrical help needed for fan
Thread Starter
CF Veteran
Joined: Feb 2016
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From: Northern New Mexico
Year: 1999
Model: Cherokee
Engine: 4.0
Hello all. I'm really not too knowledgeable when it comes to electrical. I've been trying to get my electric fan to work. I jumped the fan to the battery and it turns on. I tested the relay and it clicked but I bought a new one anyway. My friend lent me a test light. I'm not getting any power from the plug in? Bad wire somewhere in the harness? Suggestions are greatly appreciated.
Thread Starter
CF Veteran
Joined: Feb 2016
Posts: 3,683
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From: Northern New Mexico
Year: 1999
Model: Cherokee
Engine: 4.0
And when ac is on correct? Still doesn't come on. And the temp sensor is the one on the thermostat housing right?
CF Veteran
Joined: Aug 2010
Posts: 8,357
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From: Canton, MI
Year: 1999
Model: Cherokee
Engine: 4.0
Right, but the AC doesn't have to be on. If you remove the coolant temp sensor connector with the ignition switch to RUN and the fan doesn't turn on, check the following:
Note that you will get a CHECK ENGINE light on when removing the temp sensor connector. Just clear the CEL by removing the battery negative post connector for about 5 minutes.
You could check the 40 Amp Maxi fuse in the PDC to see if it's blown. See pic.

And check the #10 fuse in the Junction Block.


Verify the pin cavities in the PDC for the fan relay aren't pushed down towards the inside of the PDC and make sure the pin cavities aren't corroded (black/green).
.
Last edited by CCKen; Apr 22, 2016 at 07:18 AM.
Thread Starter
CF Veteran
Joined: Feb 2016
Posts: 3,683
Likes: 8
From: Northern New Mexico
Year: 1999
Model: Cherokee
Engine: 4.0
Thread Starter
CF Veteran
Joined: Feb 2016
Posts: 3,683
Likes: 8
From: Northern New Mexico
Year: 1999
Model: Cherokee
Engine: 4.0
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CF Veteran
Joined: Aug 2010
Posts: 8,357
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From: Canton, MI
Year: 1999
Model: Cherokee
Engine: 4.0
No, it means the fan electrical system is working - PCM, relay, fuses, wiring, and fan.
With the connector removed the PCM sees a high voltage (greater than 4.98 volts - DTC P0118) caused by an open sensor ground circuit and/or an open sensor signal circuit, which in the mind of the PCM, would mean an extremely high temp signal from the temp sensor; thus it turns the radiator fan on.
Thread Starter
CF Veteran
Joined: Feb 2016
Posts: 3,683
Likes: 8
From: Northern New Mexico
Year: 1999
Model: Cherokee
Engine: 4.0
No, it means the fan electrical system is working - PCM, relay, fuses, wiring, and fan.
With the connector removed the PCM sees a high voltage (greater than 4.98 volts - DTC P0118) caused by an open sensor ground circuit and/or an open sensor signal circuit, which in the mind of the PCM, would mean an extremely high temp signal from the temp sensor; thus it turns the radiator fan on.
With the connector removed the PCM sees a high voltage (greater than 4.98 volts - DTC P0118) caused by an open sensor ground circuit and/or an open sensor signal circuit, which in the mind of the PCM, would mean an extremely high temp signal from the temp sensor; thus it turns the radiator fan on.
CF Veteran
Joined: Aug 2010
Posts: 8,357
Likes: 103
From: Canton, MI
Year: 1999
Model: Cherokee
Engine: 4.0
Thread Starter
CF Veteran
Joined: Feb 2016
Posts: 3,683
Likes: 8
From: Northern New Mexico
Year: 1999
Model: Cherokee
Engine: 4.0
CF Veteran
Joined: Aug 2010
Posts: 8,357
Likes: 103
From: Canton, MI
Year: 1999
Model: Cherokee
Engine: 4.0
Do you own a digital Volt/Ohmmeter (Multimeter)?
If not, and there's a Harbor Freight near you, go there and buy one.
Get the 11 function digital multimeter #61593 ($24.99). Do not buy the mickey mouse $5.99 meter.
A test light won't work for the following tests.
Refer to the diagram below.
Remove the radiator fan relay.
Connect the meter ground (-) lead to the battery negative post and use the meter positive probe for the tests.
Set the meter to 20 Volts DC.
With the ignition off/lock,
Touch relay pin cavity 10 - See 12 volts.
Touch pin cavity 14 - see .000 volts.
Touch pin cavity 13 - See .000 volts.
Touch pin cavity 11 - See .000 volts.
With the ignition switch to RUN/ON (engine not running),
Touch pin cavity 10 - See 12 volts. From the 40 Amp fuse in the PDC.
Touch pin cavity 14 - See .000 volts.
Touch pin cavity 13 - See approximately .070 volts (may be lower than .070, but you must see some voltage - select 2 volt scale on your meter if you see .000 volts)
Touch pin cavity 11 - See 12 volts. From fuse 10 in the JB.
~~~~~~~~~
If you don't see some voltage at pin cavity 13 there's a possibility that the PCM driver is inop, or the wire from the PCM to pin cavity is open.

.

.
If not, and there's a Harbor Freight near you, go there and buy one.
Get the 11 function digital multimeter #61593 ($24.99). Do not buy the mickey mouse $5.99 meter.
A test light won't work for the following tests.
Refer to the diagram below.
Remove the radiator fan relay.
Connect the meter ground (-) lead to the battery negative post and use the meter positive probe for the tests.
Set the meter to 20 Volts DC.
With the ignition off/lock,
Touch relay pin cavity 10 - See 12 volts.
Touch pin cavity 14 - see .000 volts.
Touch pin cavity 13 - See .000 volts.
Touch pin cavity 11 - See .000 volts.
With the ignition switch to RUN/ON (engine not running),
Touch pin cavity 10 - See 12 volts. From the 40 Amp fuse in the PDC.
Touch pin cavity 14 - See .000 volts.
Touch pin cavity 13 - See approximately .070 volts (may be lower than .070, but you must see some voltage - select 2 volt scale on your meter if you see .000 volts)
Touch pin cavity 11 - See 12 volts. From fuse 10 in the JB.
~~~~~~~~~
If you don't see some voltage at pin cavity 13 there's a possibility that the PCM driver is inop, or the wire from the PCM to pin cavity is open.

.

.
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