• DCRC 2024

Grand Cherokee (ZJ) Battery Drain and BCM draw

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Bud

'98 ZJ
Location
Syracuse
So I have a good riddle for those that are electronics savvy.

I have a 1998 Grand Laredo, 4.0, 4wd that keeps draining the battery (just put in new one) after a couple of days sitting. Repair shop traced the problem to 180 MA draw to fuze#7, which lead them to believe it was possibly the BCM (Body Controller or Body/Chassis Control Module) and/or input keeping BCM alive and thus draining the battery. I have other "issues" and was wondering if they are related and/or would be corrected by changing the BCM:

Air Bag light comes on from time to time, but nothing comes up when scanning on OBDII port.

The radio amp little orange lights on the stock stereo go off from time to time, but doesn't seem to loose and sound amplifying.

Rear wiper doesn't work, but could just have bad motor.

Rear passenger doors electric locks will not lock/unlock, but have power to them and are trying (I cleaned out the old grease and reinstalled) to open as I can hear the motor in them actuating.

Any experts out there agree that switching the BCM will fix my problem? If so, what are your thoughts on used replacement units?

Thanks,
Bud
 
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DaveB

DaveB

Long Jeep Fan
Location
Holladay, Utah
Did they check the drain at the battery terminals before checking the fuses ? The BCM and ECM modules do draw power all the time and 180 mA doesn't seem like enough to drain the battery that quickly. I have found on several jeeps that the diodes in the alternator were allowing current to flow and drain the battery so I always check those first. There are no fuse block checks for this drain but a battery terminal test will pick it up. I have both of those modules from a 96 Grand with a 4.0 if you wanted to test the drain to see if it changes.
 
B

Bud

'98 ZJ
Location
Syracuse
DaveB, what is the best way for me to check the diodes at home with meter? If that doesn't work I will borrow your modules if they will work all right
 
F

FOURDOWN

Member
Location
Idaho Falls/Ammon
I have ran into 2 of these so far and it ended up being the rear glass ajar switch bad. about 185ma with the draw. also you should not see more than 50ma at the most after all modules have gone to sleep. i would say that replacing the BCM is not going to likely fix the problem i would get a hold of a wiring diagram for the bcm circuit and check accessory for something being on or shorting to ground or power. you may be able to find the draw by doing a good visual inspection of lights staying on like glove box,vanity lights stuff like that may not be obvious.
 
F

FOURDOWN

Member
Location
Idaho Falls/Ammon
Bud said:
DaveB, what is the best way for me to check the diodes at home with meter? If that doesn't work I will borrow your modules if they will work all right
Click to expand...

the same way that you would check for a draw at the battery in series with the circuit suspected for a draw, again you will need a wiring diagram to make this process easier.
 
DaveB

DaveB

Long Jeep Fan
Location
Holladay, Utah
Put your meter in the amp setting and put it in line with the charge line. Do this by taking off the 12V feed from the back of the alternator and putting the meter in line with the wire you took off and the terminal that the wire was hooked to. When I have found leaky diodes the current draw would usually read 500 mA or more.
 
B

Bud

'98 ZJ
Location
Syracuse
Where does the time go?!?!?!?! Okay, so I finally pulled Fuze#7 and left the ZJ sitting for over a week. Low and behold there was no battery drainage, and to my surprise it starts and drives fine without it. Only missing instrument cluster, but I drove for so many years in other vehicles with no fuel gauge, speedometer or fuel gauge that it didn't matter much to me. Put the fuze back in and it drained the battery again.

So, do you all still think it is:

1. Diode Problem
2. ECM
3. BCM
3. Stereo amp (since the three amber lights come on and off all the time?)
4. Rear glass ajar switch bad (which fuze does that go to, or where is it so I can unplug it?)

Thanks!
Bud
 
Z

Zombie

Random Dead Guy
Location
Sandy Utah
Bud said:
4. Rear glass ajar switch bad (which fuze does that go to, or where is it so I can unplug it?)
Click to expand...

I had this on my 98 5.9... and it killed my battery. pull the trim panel from the liftgate, and use a test light to find which one it is... I didn't want to lose my remote release or power locks, but I needed the drain to stop (mine would flash my dome lights when I hit a bump.) I found the right one, unplugged it, and verified that everything I wanted still worked... sorry I can't be more helpful, but it's been a while since I dealt with that repair...
 
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B

Bud

'98 ZJ
Location
Syracuse
That's plenty good info for the rear glass switch, thanks.

Anyone else have an idea on what is going on if the switch doesn't work out?
 
B

Bud

'98 ZJ
Location
Syracuse
DaveB said:
Put your meter in the amp setting and put it in line with the charge line. Do this by taking off the 12V feed from the back of the alternator and putting the meter in line with the wire you took off and the terminal that the wire was hooked to. When I have found leaky diodes the current draw would usually read 500 mA or more.
Click to expand...

DaveB, do you think I should still check the diodes?
 
B

Bud

'98 ZJ
Location
Syracuse
Doesn't look like I have an amp under the seat. So I disconnected the two rear door ajar switches for the hatch and window. Battery volt reading over last three days sitting was: 12.04, 11.94, 11.97, 11.96. I'll keep checking.
 
B

Bud

'98 ZJ
Location
Syracuse
Looks like it was the rear hatch/window ajar switch. Stayed at 11.95 all week. Should be up above 12 now that I have been driving it some. Thanks everyone!
 
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