Electrical weirdness in 97 Jeep Cherokee

My 97 Cherokee 4.0L’s battery died suddenly last week. I put a new battery in, and the next morning the car was totally dead again. I gave up and put in the shop. They assured me that the alternator, battery, and voltage regulator were all fine. However, they confirmed that there was a draw on the battery, but they couldn’t isolate it. After 3 days in the shop, they called and said it was a loose fuse. They kept it another night to be sure. I picked it up Friday, and it cranked and ran fine. Saturday morning - dead again. I’m stumped. How do you run something like this down?

Have you checked your neutral safty switch?

No - I honestly didn’t think about it. Good idea. The shop ran full diagnostics, though. I don’t know if the neutral safety switch has a sensor in the computer, though.

[i][b]battery died suddenly last week. I put a new battery in, and the next morning the car was totally dead again.

I gave up and put in the shop. They assured me that the alternator, battery, and voltage regulator were all fine. However, they confirmed that there was a draw on the battery, but they couldn’t isolate it. After 3 days in the shop, they called and said it was a loose fuse.[/b][/i]

draw on the battery,… After 3 days in the shop, they called and said it was a loose fuse.

That makes no sense to me at all.  If anyhting a loose fuese would reduce the load on the battery.  If they were really looking for a drain on the battery the ususal trick is to put an amp meter on the battery and start pulling fuses until you find the one that reduces or eliminates the drain.  It could be they did not get one back in properly that that does not explain your problesm.

That’s what they did. When they pulled the radio fuse, the amp meter showed the drain had stopped. The put the fuse back in, and the amp meter didn’t change. They repeated this several times, and kept it overnight to see if the battery drew down any. They called and said everything was fine. Should they have re-charged the battery fully before testing it? It was dead as a hammmer the morning I put it in the shop. All I did was jump it off and drive it about 5 miles. That wouldn’t be enough to charge the battery, and they never said that they had put it on a charger. I’m charging it now. BTW - there was a blue wire attached to the radio fuse. No idea what it was hooked to - probably an old cellular phone car kit.

Update: It’s now been a week and half since the battery first died. We have since been through 3 batteries, three trips to the shop (3 days each), and about $1000. The Jeep dealer’s service department is totally stumped. They know there’s a drain on the battery but they can’t find it. We’ve done everything short of totally re-wiring the car, which I do NOT want to even contemplate. Right now, it’s sitting in the driveway with a trickle charge on the 3rd new battery, which has been in for 2 days. We picked it up from the shop Friday evening. The battery was put in the previous day, and the car sat in the shop’s lot overnight and all day Friday. By 4 PM, the battery was still showing a full charge, and no drainage could be identified. We drove it Saturday - everything was fine. We probably put about 30 miles on the car. This morning, the voltage was down to 7 volts, and the brand new starter wouldn’t even turn over. I jumped the car, and the voltage meter showed a positive charge of 13+ volts with the engine running. I killed it, let it sit for half an hour, and it was down to less than 4 volts. What else could possibly cause this? Help, this is desperation time.

If you have a battery charger, I would do the following: disconnect the negative cable from the battery. Connect the charger to the battery and recharge the battery. Now, without reconnecting the battery cable, monitor the battery voltage. If it drops rapidly as it has been doing, then there is a defect in the battery. I suppose there is a chance that the battery is being overcharged and you are ruining batteries, but I can’t believe all this would happen in a week.

If the battery holds its charge, you do have a very serious current draw from what you describe. I wouldn’t park it in a garage or even near a house for fear of a fire.

You might also leave the suspect fuse out if it controls just the radio. You can live without the radio at least to see if this circuit is the problem.

It seems that the current draw isn’t constant; otherwise, the shop should have been able to find the cause. Fan motors are big current users. Sometimes, the relay(s) to an engine cooling fan will turn the engine cooling fan(s) on AFTER the engine has cooled. Other motors COULD be turning on. Periodically, sneak up on the truck and listen for fans and motors running, and lights on. If you see, or hear, any, notify your mechanic.

This is a pretty interesting one here. Sorry you have had to deal with it for so long and has cost you a lot of money.

Whatever is causing the drain it does seem it is a pretty good size current draw. I would guess a normal current draw fro your vehicle would be between 25 to 35 milliamps while the car is parked and the systems are in the sleep mode. Some systems in the car sense that the car is parked after the power is shut down for a bit and then they go to “sleep” until there is a power change and they turn on again. Perhaps this problem has to do with something waking up when it shouldn’t.

The radio may be the problem but it does draw a small amount of current normally for the memory. Maybe the ECU is causing this trouble or an alarm system possibly.

Since the trouble is intermittent and it sounds like if there is a power reset, like when the fuse is pulled and then replaced, the problem then clears it is kind of tough to track. One thing that could be done to help hunt this bad boy down is to use a DC clamp-on probe around the battery lead. This allows the current to be read without interupting the current flow and resetting the problem. Once you notice the extra current flowing then the clamp can be moved to suspected feed points from the fuse panel to pin down the exact circuit.

A DC clamp-on probe isn’t going to be in most mechanics tool boxes so you may need to go to a shop that specializes in electrical repair and see if they have one.

This is the way I would hunt the problem down at least.

I’ve got a digital multi-meter. Could I hook the probes up to the battery and just monitor them? I also bought a little LED monitor that plugs into the cigarette ligher/power outlet. I’m still concerned that the neutral saftey switch is screwed up somehow. I haven’t checked the continuity within the fuse box to see if the right contacts are hot in the right gear positions. It just seems to be an ignition problem. I don’t have anything to back that up, but the is one tough bugger to isolate. I’m also tempted to just pull the radio completely and see if that stops it. Only problem - it’s a stock radio, so I’ll have to pull practically the whold dash to get to it. The frustration is that I’ve had it at a Jeep dealership, and they should have everything necessary to run this down. Plus, I’m out 1,000 bucks, and the problem’s still there - so I’m stuck with either diving into it myself or taking it back to them for the fourth time.

You can use your meter set in the current mode to monitor the current drain. If you do it then you are going to have to pull fuses out when you see the problem happening to see which circuit the drain is on. It sounds to me from they way things are that if you find the right fuse that is in the current path and that if you replace the fuse back in then the trouble goes away. Is that correct? Hopefully your meter has a 10 amp current position.

To me the most likely suspect for this problem is the ECU or an alarm system. Something that has a processor working in it and that can change control. Things like switches and relays don’t really do that by themselves.

Pulling the radio out isn’t real hard if it is like our '95 model GC was. You just remove the front cover of the console and then can get at things from there. I wouldn’t remove anything until you know for sure the area that needs attention.

I think it is good you want to tackle this yourself and hope you find the trouble. I would not take it back to the shop you have been using since they are just costing you money. If you need to take it in take it to a place that specializes in electrical repairs. They will find the trouble.

Hey, Guys. Thanks for all the tips. I printed them out and took them to the shop. The tech seemed happy to have some suggestions.

They found the drain: somebody had wired a kill switch into the line going to the a/c clutch. Evidently a previous owner was too cheap to buy a new dashboard switch, so he went to Radio Shack and wired kill switch in line to the a/c. I guess they would open the hood, flip the switch so they could have a/c for a while, and then reverse the process when they got whre they were going.

The only way we found it was one of the techs drove the truck around, and when he killed it and got out, he noticed a humming sound under the hood. So, they traced the wiring harness until they found a wire that wasn’t supposed to be there. So, hopefully the problem is solved - we’ll see.