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Dan
Dan, Technician
Category: Jeep
Satisfied Customers: 23591
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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I am troubleshooting a cooling fan problem. Cooling fan

Customer Question

I am troubleshooting a cooling fan problem. Cooling fan comes on when jumpered to 12 v. Disconnected fan relay module and ran car until overheated. Tested signal telling the relay to come on....no voltage. help
Submitted: 9 months ago.
Category: Jeep
Expert:  Dan replied 9 months ago.

The PCM is what grounds signal wire so this either means PCM has failed or blue/pink wire that goes between PCM and relay is broken. Disconnect PCM and ground the blue/pink wire at pin 17 of connector 2, if fan comes on replace the PCM. If fan does not come on run a new wire between relay and PCM. Let me know if you have more questions or if there is anything else I can do to help. Thanks.

Customer: replied 9 months ago.
I should not expect a 12 v signal on that wire going TO the relay?
Expert:  Dan replied 9 months ago.

No, the PCM activates the relay with ground. The gray wire should have battery voltage and black wire should have constant ground. Let me know if you have more questions, thanks.

Customer: replied 9 months ago.
I am confused. On the Jeep,the black is ground....blue/pink is the control from the PCM,............Green is out to the fan....and gray is the fused 12v from the battery. The way I understand solid state relays is that the control signal is ON and that allows the current to flow to the fan. Where am I mistaken? Please help.
Expert:  Dan replied 9 months ago.

You are right on everything other then blue/pink wire. The PCM provides blue/pink wire ground which activates the relay, not power like you thought. Let me know if you have more questions, thanks.

Customer: replied 9 months ago.
Wondering....on that control wire (blue/pink), when the PCM is NOT grounding that wire to the relay, should there be any voltage reading on it?
Expert:  Dan replied 9 months ago.

No there should not be voltage on that wire at any time. Let me know if you have more questions, at this point I'd do the above test to determine if problem is wiring or PCM. Keep me updated, thanks.