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Volmeter drops and check gauges light comes on....what gives?

hopper720

NAXJA Forum User
Location
Connecticut
Hey all,

I have a 97 XJ I6 and recently i've noticed that when i start it up all the gauges look fine and then a few minutes into driving, the voltmeter goes all the way down and my check gauges light comes on.

I had my battery checked, ( it needed to be changed) and my alternator ( guy said it was fine). I swapped out the battery with a brand new one that i had, it was for a newer cherokee, so it was a bit larger but I just wanted to see if it would fix it. Put it in, started driving and the same thing occured.

Any ideas on what this could be?
 
interestingly enough my 99 was doing that the other week, i work at a auto shop so i did several load test on the alternator which checked out fine, i was able to pull into work one day when the gauge had dropped out, so i checked the voltage at the battery with my multi meter, 13.8V, checked the voltage at the PCM with the snap on scanner, 13.8V, so i figured it was a cluster issue. i removed the cluster and cleaned the 2 connectors for the cluster with some contact cleaner and compressed air, its been fine for over 2 weeks.
 
When that happened to me, my alternator was going out. When the gauge drops out, check the voltage on the battery to confirm it's around 14V. Anything less than 13V I would change the alternator.
 
I had the same problem as crimsondragon.

This issue has been coming up a lot just recently, and I think perhaps it reflects the overall aging of the fleet. Our alternators are all wearing out at once!

Anyway, the first thing you should know is that if the voltmeter drops, due to a bad alternator, etc., after a short time it will drop to zero and set the "check gauges" light. That's a feature, like it or not. I think it's stupid to disable the voltmeter at the very time you need it most, but some clever engineer at Jeep decided to turn our gauges into idiot lights with needles on them.

So there you are, with your alternator dead, wondering if you have enough juice left in the battery to get home before the engine conks out, and the one thing you need - a functional voltmeter - has been switched off! Thanks a lot, folks.

Things you can do when this occurs: first, if you have a hand held voltmeter, check the voltage at the battery while it's running. If it is not up around 14 volts, then it's not the gauge cluster's fault. Second, find a stick or something with which you can safely hit the alternator while it's running. If it pops back, you have bad brushes, and it's time either for an alternator repair or a new alternator (depending in part on whether the slip rings are gouged up). Finally, if you get good voltage at the battery while the gauge is misbehaving, assume a bad connection at the cluster and address that.
 
There is a known issue with the plug on the cluster. It can get loose. Take cluster out clean reassemble. Usually fixes that. There are plenty of threads on it as well.
 
An intermittent alternator might test as OK. And the bench testers in a parts store are not 100% conclusive either.

Best thing to do as mentioned is freshen engine grounds, then keep a meter with you (everyone that works on their XJ should have one) and when it happens, pop the hood and verify it at the battery.

If it truly has dropped in output, this is most likely a failing alternator.
 
Alright so here's an update:

I Changed my alternator today because when i had it checked by the guy at the auto parts store said it was charging a little week.

AFter all was said and done fired it up and went driving and sure enough, about 2 minutes into the drive the voltmeter dropped all the way down again.

I pulled over and tested the battery and alternator. Both the battery and alternator were reading around 12 (with the car on and off). SHouldnt the alternator be up around 14 when the car is running? and just the battery around 12(when the car is off)?

So now I dont know what to do....fresh battery, new alternator....i took the gauge cluster off and it was clean as a whistle and then re-plugged it back in.

DOes any one have any other suggestions?
 
yes, 12V is battery voltage (actually should be closer to 12.5) you should be reading somewhere around 14V while the engine is running. Wish I had a test procedure or even a wiring diagram for ya... even the FSM is fairly worthless when it comes to actually telling you what the field connections are (does it charge by grounding the field or applying voltage to it? I dunno. I guess if you don't have a DRB III you are screwed?) Do you have any codes? How is the big fat wire w/ fuse link between the alt. and PDC? that would be an easy fix if that were your problem.

FWIW I believe on a '97 the voltage regulator is part of the PCM; worst case scenario you might have a bad PCM... but I would first try cleaning the connections to the alt (I assume that you have done this already) and then the PCM; make sure that the wires between the two are not broken.
 
All the connections to my alternator are good because when I just put the new one in I made sure that everything was clean and connected well. If the PCM is the computer on the driver side of the engine bay, yea i unplugged all of those and plugged them all back in.

I dont know if any codes are coming up because i don't have one of those obd scanners.
 
I dont know if this bit of knowledge makes a difference or not but the current PCM that is in the car is not the original that came in the car. WHen I first bought the jeep about 4 years ago I shorted out the original PCM like an idiot and was able to find a replacement one in another jeep. Havent had a problem since, but do you think there could be a problem with it now?
 
Just had the same problem with my 2001 xj. Mine turned out to be my alternator.

The pcm regulates the voltage in your charging system. As long as you know beyond a shadow of a doubt that all your grounds, fuses and most of all the replacement alternator are all good, you may very well have a bad pcm. But a voltage fault in the pcm usually throws a check engine light. Very rare.
 
all you talking about the grounds on the jeep itself? The braided one and the one on the passenger side fender? Those are good. The fat fire that connect to the alternator is on their tight...where does the other end connect, maybe the problem is there?

I went through the fuses and looked at ones that i thought might make a difference. Any fuse in particular to look at to make sure its good?

The new alternator should be good. I just bought it today. Im sure there are times where the alternator out of the box isnt good, but what are the odds?
 
all you talking about the grounds on the jeep itself? The braided one and the one on the passenger side fender? Those are good. The fat fire that connect to the alternator is on their tight...where does the other end connect, maybe the problem is there?

There is one more that goes onto the block directly from the battery, and one on the dipstick tube, and another right next to the one that connects to the block directly on the passenger side, next to the coil

I was fighting this same problem on my 99 in december, volt meter would drop. Some time hard starts. I was convinced my alternator was flaking out. Until I realized my ground cable going from the battery to the block directly was loose and the bad connection literally welded the nut onto the stud. I went to auto zone and got 4 gauge wires and replaced all the + and - cables. 3 grounds and 3 positive cables total. Also i replaced the oem terminals with marine ones with the wing nuts on top.

Edit: the ground that goes on the dipstick tube and the other smaller ground wire near the coil are part of the wiring harness.
 
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Is the belt slipping? I've had mine do that on cold mornings. Every stopsign / light the belt starts slipping and it says to check gauges.
 
To go along the belt slipping.. when my water pump seal started to go my voltmeter dropped to zero due to the belt slipping. I'm assuming that this isn't what your seeing but worth a shot.
 
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