Voltage problem for 1999 XJ 4.0 2WD
#1
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Year: 1999
Model: Cherokee
Engine: 4.0
Voltage problem for 1999 XJ 4.0 2WD
I have a strange issue with my 1999XJ 4.0 2WD. I was driving down the road and at about 1/4 mile the battery light came on. I noticed that the headlights were a little dim. I pulled into the nearest gas station and checked the voltage at the battery while the vehicle was running. It read 12.11v. As I revved the engine the voltage dropped 12.10 then 12.09. I stopped revving the engine and the voltage went back to 12.11. I had just replaced the Alternator on Saturday. After replacing the alternator the volt meter read 14.20v. The vehicle worked fine all weekend and then yesterday I was headed down the road at about 1/4 miles and the battery light came back on. I repeated the previous voltage check and once again the voltage read 12.11v and had the same results as before. I was told by the Advance Auto Parts guy that the voltage regulator was in the PCM and this could be the issue so I just thought to wiggle the 3 cables that attached to the PCM. The voltage jumped back up to 13.80v and when I revved the engine it would go to 14.20v. This is a strange thing due to the fact that I had recently cleaned and reconnected the cables to the PCM along with putting dielectric connector grease to make a good connection. The battery light never came on again for the rest of the 25 mile trip to work. I need to know which cable has the wiring for the voltage regulator in it. It could have been a bad connection somewhere on that line or at the PCM. When I leave work today I will check the voltage again to make sure it is running right. All the connections are good at the alternator.
#2
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I would check to see that your dielectric grease isnt making connections between other contacts.
I would then follow the wire looms and look for any wear.
Clean grounds, retighten alternator connections.
The ECU rarely goes bad, So I wouldnt really be looking at that.
I would then follow the wire looms and look for any wear.
Clean grounds, retighten alternator connections.
The ECU rarely goes bad, So I wouldnt really be looking at that.
#3
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Year: 1999
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Checked connectors and wiring harness.
I would check to see that your dielectric grease isnt making connections between other contacts.
I would then follow the wire looms and look for any wear.
Clean grounds, retighten alternator connections.
The ECU rarely goes bad, So I wouldnt really be looking at that.
I would then follow the wire looms and look for any wear.
Clean grounds, retighten alternator connections.
The ECU rarely goes bad, So I wouldnt really be looking at that.
Last edited by lavendje; 01-19-2011 at 08:11 PM.
#4
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Year: 1999
Model: Cherokee
Engine: 4.0
Third day of crazy voltage.
This morning while the vehicle was cold the temp was 33F I checked the voltage after cranking the vehicle. It read 14.17v so I thought it was ok. I put the car in gear and drove 1/4 mile and the battery light came on again. I pulled into the same gas station and checked the voltage which read 11.89v with the lights and everything on then all of a sudden without doing anything I hear a sound like something kicked in and the voltage jumped up to 14.01v. This is getting to be very strange. When it snowed I could have gotten water in the PCM when I had the hood up slightly charging my battery. There is a little hole in the back of the PCM. I am going to have to take it off the mount and see if water comes out the hole.
Last edited by lavendje; 01-20-2011 at 08:02 AM.
#6
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Year: 1999
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I replaced the battery 5 or 6 months ago. The battery tests good and will take a full charge and still has 950 cold cranking amps. I had a starter issue which I thought was a battery issue. It turned out the starter seized. Could water in the PCM/ECU have any effect on the voltage issue? I would hate to have to spend another $190 on a rebuilt PCM/ECU.
Last edited by lavendje; 01-20-2011 at 09:39 AM.
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#8
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Year: 1999
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PCM/ECU
Well it looks like its the Voltage Regulator in the PCM/ECU. We did a lot of testing and it is coming back to the $187 PCM/ECU. Does anyone know of a cheaper priced on the web?
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Year: 1999
Model: Cherokee
Engine: 4.0
As the computer is pretty hardy, I would certainly consider getting a salvage yard one.
Probably in the $30 range. Check with your local salvage yard and even if they don't have one, they could probably have one for you in a day or two.
Probably in the $30 range. Check with your local salvage yard and even if they don't have one, they could probably have one for you in a day or two.
#10
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I would but the PCM/ECU has to match you vehicle exactly so each one is programed for each vehicle type, power requirements, and accessories.
#11
A new PCM will need to be re-flashed by the dealer so that the VIN in the PCM matches the VIN in the gauge cluster.
Simply dropping a PCM in will cause the CEL to come on.
Simply dropping a PCM in will cause the CEL to come on.
#13
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#14
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Year: 1999
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PCM/ECU
I have found a used PCM/ECU for a 99 Cherokee 4.0 W/Automatic Transmission. It came off of one that was running fine until it was totaled. I haven't put it in yet but I will after work and see what else can go wrong.
Last edited by lavendje; 01-24-2011 at 10:09 AM.