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Chrysler Repair/'01 Minivan Voyager: P1491 Code, radiator fans relay control circuit

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QUESTION: The Voyager is showing code p1491-rad relay problem.  There is a harness that runs from the left headlight to the fuse panel (i believe called pcm) that includes relay wiring and it is mangled.  I replaced the wires to get lights back working, and the red 12AWG wire for relay, and blue-violet 18AWG wire for relay both going to pcm.  The fans kick on when up to temperature, but still get 1491.  
The Bk/GN (18AWG)wire is grounded, but not sure if grounded because of mangled harness.  I couldn't find where this wire goes to replace it.  I couldn't find a schematic of this circuit, best i could do is trace wires.


I believe the red is 12VDC constant power to relay, and when temp reached, closes and energizes blue 12AWG wire to run fans.
I'm not sure how the control wires (18AWG) are supposed to act, if they are feedback to the controller, and temperature is what closes the contacts to turn the fans on and tell what state they are in to the computer, or if they are the coil for the relay and the computer energizes them to turn on relay and fans?

What should i expect to see on the control wires when the fan is on and when it is off?  Also, any idea where the black/green wire goes so i can replace this?

Thank you in advance for any help,

Regards,
Joe

ANSWER: Hi Joe,
You have the wiring concepts correctly. Have you tried disconnecting the battery for a minute to erase the stored code, and then driving it some to see whether it returns? A code 1684 will show up (it means battery disconnected recently).
The orange/red wire to the relay is 12v constantly from the battery via fuse 27. The dark blue/dark green wires power the two fans. The black/dark green is the relay activation coil grounding wire that goes to a splice that is along the structural member that goes under the radiator which joins it to the fan ground wires and thence to the ground point near the headlamp.
The relay activation is accomplished by the pcm putting 12v on the dark blue/violet wire that comes from pin 1 of the green/blue plug at the fuse box. It does that when the coolant temp sensor tells it or you request A.C.
So I think you have the problem resolved as it stands, you just have to clear the fault code.
Please read the PS below and respond to it.
Thanks,
Roland


---------- FOLLOW-UP ----------

QUESTION: Roland, Thanks for the quick reply.
So the black/green wire can be grounded anywhere, it the pcm doesnt need to see it anywhere?

I drove the van a few miles so that the fans would kick on, shut it off, restarted it to get to temp, and tried resetting with an obd scanner. I believe i had the battery out also, need to remove to get to connectors.  

It sounds like there is no feedback from the relay then.  guessing the code is generated if control wire is open (no current flow on blue/violet) or shorted to ground?

I am also assuming that if the fans are turning on and off that the relay is good, and all my wiring is good?
From everything i've read it looks like this relay and temp sensor are all that will generate this code.  

Thanks for your quick response.  Will try disconnecting battery when i get home tonight.  if it still doesn't clear might try running the black green wire to a solid ground.  

Appreciate your help.

Joe

Answer
Hi Joe,
The black/dark green is on one end of the activation coil, and the pcm puts 12v on the other end to close the relay. If the grounding wire were flakey then the pcm would notice that because the relay wouldn't close (there would be no flow through the activation coil) so that might explain the persistence of the 1491. You can ground the wire to the splice where the fan ground wires go, under the radiator, or connect it to the ground at the headlamp. Or the dark blue/violet wire might be intermittently grounded due to short in the wire, which would also be noticed by the pcm and set the code. But if the fans are working then at that moment the activation circuit is 'solid'.
I would appreciate your doing a rating and 'nomination' of me for these answers.
Thanks,
Roland

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Roland Finston

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