P1491 code

[uss2defiant]

Hi all,

Noticed my radiator fan was not working a few days ago.

Was working on it this morning when I noticed the CEL.
got a P1491 error which is the radiator fan control relay circuit.

However, after inspecting the e-radiator fan, I noticed that one of the wires was sheared in the middle. This was probably caused by the incorrect clutch fan that I had on for a short period when I replaced it.

I had a new e-radiator fan with me. I cleared the CEL fault and plugged the new fan in. Ran the jeep on idle till the temp rose but the fan did not kick in.

I've checked the fuse. Disconnected/reconnected the radiator fan control relay circuit.
I have not checked the other relay on the junction block.

My questions are:

1. I did notice that right from the get-go at cold start, the female plug to the e-rad fan was outputing 12V. The AC was off and this doesn't look right to me. Thoughts on this?

2. Will the P1491 error pop out if the e-radiator fan is not working?

I've yet to look into the wiring from the PCM to the relay. Going wait till it cools down so I'll trouble shoot it in the evening.
Thanks.

 

[ltd02]

Any luck on troubleshooting? I had this code one time but it was only a bad fan relay. Wound up with a new set of headgaskets as a result so not trivial at all.

 

[uss2defiant]

No. Just got done trying a 2nd relay. Both times with a new radiator fan.

The lines to the relay and fan were fine except for the control line to the PCM.
Not too sure what to expect. Still getting NIL from that. Is that suppose to be a 12V control line from the PCM?

With the first autozone replacement part, I was reading 9V to the fan from a cool engine to a hot engine at 200F.
I didn't get a chance to do more debuggin with the o'reilly part as it was getting dark out. I don't have a garage.

I've tried two different relays. One from autozone and one from O'reily. I think the chance of 2 different parts failing is very unlikely.

The fan should have kicked on when the coolant is above 176 F or 203F w/ the AC on. Nothing came on.
The jeep also died suddenly. It erased the CEL code so there's some electrical gremlins.

I still have the P1491 code.

I don't think it's the coolant temperature sensor as it seems to read fine on the obd.
Could it be the battery temp sensor?


HELP! HELP! HELP!!!!!

All I can do is to wait till the MOPAR part gets here.

 

[uss2defiant]

Any luck on troubleshooting? I had this code one time but it was only a bad fan relay. Wound up with a new set of headgaskets as a result so not trivial at all.

Did you use a MOPAR part?

 

[uss2defiant]

I found this for that PWM signal from the PCM to the relay as the control line.

[YT]AdIYm9kM5E0[/YT]

Anyone know anything about the PWM parameters?
Can't seem to google anything.

 

[uss2defiant]

Anyone know the MOPAR part number?
Not getting anything from google and the usual dealership parts guy I deal with is coming up NIL.

 

[uss2defiant]

NVM
Finally after some googling, got it verified as 68023333AA

 

[ltd02]

Did you use a MOPAR part?

Sorry, no access at work. Dealer changed it. Mine went in traffic on route 355 in Gaithersburg MD on my way to work. It overheated before I could get it out of the travel lanes. I limped it to a Jeep dealer that I had dealt with before and they were great. They squeezed me in quickly and replaced the relay for about 160. I thought it was a bargain considering the circumstances. Unfortunately the HGs were toast by that time but the relay worked great :gr_grin:

The images from the number you have looks just like the one I have.

 

[uss2defiant]

okay.Thanks.

I'm getting some print outs from the FSM to debug the PCM and redo some of the debugging I did.

Fingers crossed.

I decided to hold off on ordering a MOPAR replacement until I can for certain eliminate the PCM.

 

[uss2defiant]

Here's what I did tonight. Please excuse the caps. The caps just highlight items, not shouting.

1.
so I went down the list from post #2 from a grand cherokee forum

Check Engine Light (CEL) - P1491 - Fan Relay Circuit

Everything checks out.

2. reconnected radiator fan and ran the jeep till coolant hit 176F. If I'm not mistaken that's when the fan should kick in without the AC. With the AC I had to wait till 203F.

FAN DID NOT TURN ON

3. disconnected relay and probed the voltage on the control line from the PCM. It read 0.28V with the AC off. Value did not change when AC was on.

ANYONE KNOWS WHAT I SHOULD BE READING? NOTHING IN FSM. CAN'T FIND SOLID ANSWERS ONLINE.

----
I'm starting to lean towards a PCM problem but everything else seems to be working fine.

THOUGHTS/COMMENTS?

My plan is to put everything back together including the original relay and just run it. Maybe the CEL light will come back on? idk.

 

[ltd02]

Just be careful of the overheat. Didn't take much to cook my HGs. Never even made to the max. I'm not sure of the "fan on without AC temp" but thought it was higher than 176. I read somewhere (TJKJ I think) that the temp was 219 without the AC on.

Did you put 12v to the new fan? Maybe it is defective. Like you said the AC on should have done something at least temporarily.

 

[uss2defiant]

Yeah. I shorted the two pins. My old radiator fan works after repairing the wiring.

That's correct. AC + 210F I think would turn it on.

I wonder whether it could be the other temp sensors.
There are the battery temp sensor and the coolant temperature that is used for the turn on conditions. Thoughts?

 

[uss2defiant]

Time to bust out the oscilloscope.
looks like it's a negative PWM to the relay.

Trouble shoot electric fan - Dodge Ram, Ramcharger, Cummins, Jeep, Durango, Power Wagon, Trailduster, all Mopar Truck & SUV Owners. Dodgeram

Anyone knows how to get the TSB for the debugging?
Thanks.

 

[ltd02]

Time to bust out the oscilloscope.
looks like it's a negative PWM to the relay.

Anyone knows how to get the TSB for the debugging?
Thanks.

Maybe you could just wire the fan to a switch for now. At least it won't overheat and you can use it while you debug.

 

[uss2defiant]

Maybe you could just wire the fan to a switch for now. At least it won't overheat and you can use it while you debug.

I have a clutch fan so I'm not too worried.
Did your liberty also have a clutch fan before you had the HG problem?

 

[uss2defiant]

What are the chances of the radiator temp sensor and the battery temp sensor are bad?
There's a CEL code for both but none have shown up.

I haven't had the time yet to use the oscilloscope to probe the PWM signal from the PCM yet. I've put the old repaired radiator fan back (verified it works) and the old relay back on. No CEL yet.

:shrug:

 

[ltd02]

I have a clutch fan so I'm not too worried.
Did your liberty also have a clutch fan before you had the HG problem?

Yes I had the clutch fan. I was stuck in traffic and it just couldn't keep up I guess. I know some people will say or testify otherwise but that clutch fan isn't designed to be the sole cooling fan.

 

[uss2defiant]

Yes I had the clutch fan. I was stuck in traffic and it just couldn't keep up I guess. I know some people will say or testify otherwise but that clutch fan isn't designed to be the sole cooling fan.

I agree with you on that.

 

[uss2defiant]

so is the dealership the only place capable of verifying that the PCM is the issue?

 

[ltd02]

so is the dealership the only place capable of verifying that the PCM is the issue?

There are probably places out there where they could diagnose but that's an item I would probably trust to a dealer. I say that because I have two Jeep dealers in my area that I trust and have been great to me.