1998 Jeep Cherokee electrical problem

OUTLAW10

MEMBER
1998 JEEP CHEROKEE
6 CYL
4WD
AUTOMATIC
225,000 MILES

I have a 1998 Cherokee sport and I am having trouble with something draining down the battery. I have checked the alternator, replaced the battery, and checked every fuse in the front left hand side under the hood and the fuses located on the passenger side of the vehicle. I disconnected the neg cable from the negative post of the battery and connected my test light to the neg cable and then to the neg post. It remained lit throughout the entire process of pulling each fuse except fuse #15. When I pulled fuse #15 the light went out. The manual said that this procedure would tell me if I had a short in the circuitry. I believe that fuse controls the dash gauges. If I start the engine and then pull that fuse all gauges go out. I do get a light that tells me to check gauges sometimes not always when I am driving the vehicle. So what exactly am I looking for behind the dash? And is there a possibility of activating the SRS system and causing the air bags to inflate while I am trying to get the dash assembly off? Thank you
Rick

1 Reply

CARADIODOC

MECHANIC
33,873 POSTS

First, forget the air bag. You have to really try to make one pop. The second problem is with your testing method for the drain. You didn't say what the symptom is or how long it takes to kill the battery, so I can only offer a suggestion on your test method. Some vehicles have computers that can take up to 20 minutes to time out and go to "sleep" mode. Until that happens, they can draw up to three amps.

What you need to do is insert an amp meter between one battery post and that cable clamp, but you have to start out on a high enough scale to prevent blowing its internal fuse. That's commonly a 2-amp fuse. You have to start on the 10-amp scale which usually means moving the positive probe to a different jack. Once you see the current drop after about 20 minutes, you need to move the probe back to the regular jack for more accuracy on a lower scale, but that means momentarily opening the circuit. Opening the circuit wakes up the computers, then you have to start all over waiting for them to go to sleep mode. That can blow the 2-amp fuse too.

To prevent this issue, use a small jumper wire to bypass the amp meter until the 20 minutes is up. After that, remove the jumper wire and verify the reading is low enough to switch to the lower scale. Once you see the current is low enough, put the jumper back on, then move the lead to the regular jack. Now you can remove the jumper and watch the reading.

The next problem comes when you want to switch the meter's switch to a lower scale for more accuracy. All meters use "break-before-make" switches. That means the switch breaks the circuit momentarily, then makes it to the next scale. That momentary break again can wake up some computers. To avoid that you must again use the jumper wire when changing scales.

Once you get to the lowest scale, the magic number is 35 milliamps, (.035 amps). If you find less than that, a good battery will still be able to crank the engine fast enough to start after sitting for three weeks.