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Power Module issue

B

BostonIrish

NAXJA Forum User
Location
Cape Cod
My kids 99 Cherokee was acting up power locks not working..dome light not shutting off and then one morning it wouldn't start.I tried isolating a bad ground, replaced the door switches..nothing.I brought it to a garage who then sent it to the dealer who couldn't figure it out.They said the neg battery cable was cracked? I think that's a crock as they said the power module under the hood might be the issue and in that case it's not worth repairing due to the cost? I've had 7 jeeps and a couple of Cherokees ..never seen a power module go bad?
 
Issues with failed wire splices and short/open circuits in the door wire harness are very common, and can cause some or all of the symptoms you describe.

If the battery cable needs replacing, replace it.

WTF is "power module" ?
 
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My bet is that the power module refers to the fuse center/block under the hood. Yeah, I doubt that's "bad."
 
Guessing that's the Powertrain Control Module... I wouldn't take the Jeep back to that mechanic or that dealer again, FWIW.
 
Under the hood there is no "power module" as to my knowledge and I work at a Jeep dealer. Now there is the power distribution center but it is simply a bunch of wires running through a central point but it is not really something that can go bad in itself. I would definitely think that something is not properly grounding somewhere. Try replacing the negative battery cable, the chassis ground, and maybe even the engine block negative ground strap.
 
I replaced the neg cable ..Im not sure why the lights are staying on ..I heard the CPS sensor could shut down the PCM if its bad too.I thought the dealer could have figured it out.We are picking it up Monday..Im hoping no more fuses blow and this is over with..I hate throwing in parts by just guessing at the issue.
 
BostonIrish said:
I replaced the neg cable ..Im not sure why the lights are staying on ..I heard the CPS sensor could shut down the PCM if its bad too.I thought the dealer could have figured it out.We are picking it up Monday..Im hoping no more fuses blow and this is over with..I hate throwing in parts by just guessing at the issue.
Click to expand...

You know what now that you mention it I have heard of the issue with the CPS as well. The guy unplugged his CPS and the issues he was having went away. Try unplugging the CPS when you get it back and see what that does for you lights. Otherwise it could be something more directly involved with the door harness or even the door switch for the dome lights. I might even try unplugging the each door harness and see if that helps.
 
Lights have abso-freakin-lutely nothing to do with the CPS on an XJ. Nothing. Maybe on a ZJ/WJ, but not on an XJ.

CPS will occasionally confuse the ECU enough that it won't communicate via CCD with the instrument cluster (leading to a "no bus" display on the odo) but that's about the worst it will do, aside from of course not letting the engine run.
 
That's what's driving me nuts..I tried replacing the door switches..found no breaks in the door harness..kept blowing the inst.panel fuse and then one morning it wouldn't start.I even pulled the rear hatch apart..my kids gonna pick it up Monday.Im down in Florida..so I'll get a better idea of what the dealer did when I get back.
 
It died again...the alarm wouldn't stop...going off so I had to disconnect the battery.I disconnected the power lock switches that were making a weird noise when I reconnected the battery.I drove it around after replacing the fuse...semmed ok..this morning the battery was dead? I have no idea what is causing this drain!
 
sidewaysstarion said:
I think the mechanic might be thinking about a BCM which was used on the Grand Cherokees. But yeah, it sounds like a bad door harness.
Click to expand...

While trying to guess what "Uncle Bob" the moron is talking about, you are probably on the right track and "Uncle Bob" thought there was a BCM in the XJ.

"Uncle Bob" is a true moron.
 
BostonIrish said:
It died again...the alarm wouldn't stop...going off so I had to disconnect the battery.I disconnected the power lock switches that were making a weird noise when I reconnected the battery.I drove it around after replacing the fuse...semmed ok..this morning the battery was dead? I have no idea what is causing this drain!
Click to expand...

1. Find the parasitic drain. Search Google/youtube--thousands of DIY articles/videos.

2. When in doubt, follow the instructions in No. 1 above.
 
Agreed, it sounds like you need to start pulling fuses. I like to put my meter (or an incandescent test lamp - an LED one will illuminate even with a reasonable ignition-off draw, so they don't help much) in between the positive battery terminal and the cable, then watch the current draw as I go through the power distribution center (fusebox under the hood) pulling one fuse at a time. When the current drops significantly you have found your draw. The IOD fuse (ignition off draw) should draw only a few tens of milliamps on an XJ, the rest should be basically zero with the key out and lights off.

The last time I diagnosed an issue like this it was on a friends 98 XJ and it ended up being the stock amplifier under the back seat for the luxury package sound system it came with. Unplugged that and the mystery draw was gone.
 
BostonIrish said:
It died again...the alarm wouldn't stop.......the power lock switches that were making a weird noise when I reconnected the battery...this morning the battery was dead? I have no idea what is causing this drain!
Click to expand...

A failed alarm unit or a crappy install can cause wiring issues or short circuits/open circuits. Aftermarket alarm, or Factory/Dealership installed ?

Power locks making noises by themselves and a drained battery points toward a short circuit of some type. Inspected the entire drivers door wire harness yet ?
 
Yeah...I pulled both doors apart..the IOD fuse under the hood blew before and I think if I leave it in ...kills the battery.The power lock fuse 25 amp was blown on the interior fuse box.The alarm is factory and just randomly went off by itself..I had to pull the battery cable at 1am...I drove it around the next day for a bit and the next morning the battery was almost dead..I have both those fuses out and Im gonna try to restart it once the battery is charged.Both the door harnesses looked good...The dealer couldn't figure it out but they also left 1 powerlock connector off and half the screws in the interior were loose as hell.
 
BostonIrish said:
Thanks...what's with the Uncle Bob reference?
Click to expand...

"Uncle Bob" is from the part of the family tree that doesn't have any branches. He divorced his wife, but she was still his sister.

"Uncle Bob" is the moron that screws things up by "fixing" them, making the problem worse by a value of 10.

Avoid "Uncle Bob".
 
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