Rubicon Owners Forum banner

1 - 14 of 14 Posts

·
Moderator
Joined
·
1,323 Posts
Discussion Starter #1
My 2004 was running fine, but the battery died. Replaced and good, but then after about a minute I throw a P1594 - Charge system voltage too high.

From what I read it could be...
The Battery Temp Sensor...I don't think so.
The alternator...maybe
The PCM (regulator)...I hope not! I don't think it is. I didn't have this code with the old battery.

Honestly, it started with the new battery installed.
I'm going to do some troubleshooting, but do any of you have insight on what may be going on?
 

·
Moderator
Joined
·
1,323 Posts
Discussion Starter #3
That’s what I was hoping. I’m going to pull it, check the temp sensor, and reinstall. I’ll check the output of the alternator.
 

·
Premium Member
Joined
·
1,201 Posts

·
Registered
Joined
·
484 Posts
Make sure your connections are good. Including grounds. Then actually check the voltage at the battery and then the alternator output wire, are they the same?
 

·
Moderator
Joined
·
3,336 Posts
Make sure your connections are good. Including grounds. Then actually check the voltage at the battery and then the alternator output wire, are they the same?
A direct, and separate ground to the alternator case is always a good idea as well.
 

·
Moderator
Joined
·
1,323 Posts
Discussion Starter #7 (Edited)
Thanks all. I’ve been studying like crazy. It’s not that alternators are difficult. It’s that my charging system is acting strange.

All began upon installation of a new battery.
What am I seeing?
A message of overcharging.
Battery via meter post to post - 12.3
Engine running - 12.3
Engine at 1500 RPMs 12.3 at alternator output
Alternator output engine running - 12.3
Dash dummy gauge - 14.5
Scanggauge - 11.5

My old battery when good measured 13-14 consistently via Scangauge.

According to the FSM, after getting the code and inspection...
Disconnect PCM connections.
Disconnect alternator field plug.
Measure the K20 to ground resistance.
If less than 100 ohms, repair short to ground.
I actually measured 0 ohms which means I need to repair a short. I can’t wrap my head around why the FSM says I should measure over 100 ohms with everything disconnected. I understood my past injector plug short and resistance. Tomorrow I’m going to visit a mechanic that has been relentlessly successful in problem solving and he has up to date scanning abilities. We were talking today and both scratching our heads.
 

·
Moderator
Joined
·
3,336 Posts
Th3 reading of 12.3 volts at the battery while running is too low. I find it odd that the dash is showing 14.5, but if that is what the PCM believes is the battery voltage, then it might explain the charging issue.
 

·
Moderator
Joined
·
1,323 Posts
Discussion Starter #10
Took it in to the Jeep mechanic that handled my earlier PCM problem. The alternator is running wide open at 15 volts, but is not charging the battery. According to the wiring diagram, there’s a fuse able link that I may have blown when I changed the battery. He said that you can look at it and not be able to tell if it’s blown. He also wants to validate the wires from the PCM to the field plug. I’m not sure if I heard him correctly, but he also said he was able to talk to the charging system through the PCM via his computer, but cannot rule out a PCM problem just yet. The things I like about this guy is he’s an investigator, he explains his investigative process, and resists buying unnecessary parts.

This morning was off the clock. I’m taking it back Monday when he’ll have time to go over everything.
 

·
Administrator
Joined
·
10,476 Posts
Sounds like your mechanic is doing a good job of troubleshooting, I like the idea of a blown fusible link - finding it might be a problem since it might be almost the same size as the primary wire from the alternator and/or battery.
 

·
Moderator
Joined
·
3,336 Posts
According to the wiring diagram, there’s a fuse able link that I may have blown when I changed the battery. He said that you can look at it and not be able to tell if it’s blown.

A simple continuity test, ohmmeter across the link will tell you if it's good or not (make sure there is no voltage on it first)
 

·
Moderator
Joined
·
1,323 Posts
Discussion Starter #13
UPDATE - The PCM had to be replaced under warranty. It was not regulating voltage correctly. My Scangauge said one thing. The dash another. The alternator was running wide open and not charging the battery. Now all is fine.

Here’s where it got a little dicey. Autozone could not find another PCM and offered to get it fixed for $90. YEAH RIGHT! Autozone also offered our money back. The mechanic and I told them to keep looking. Meanwhile the mechanic found another PCM source and in his words, they bought the warranty from Autozone and replaced the PCM. All this didn’t cost me a cent. I was expecting to pay some type of diagnostic fee, but nope. It was all under warranty.

If I was younger, I’d figure out how to make these PCM’s. Somebody could make a killing.
 

·
Administrator
Joined
·
10,476 Posts
Yikes - another PCM bites the dust! :surprise:
Vehicles used to be so simple, the alternator had the voltage regulator in the case. You have to question the wisdom of putting all of the eggs in one basket (the PCM controls everything.)

Thanks for the followup - glad you're up and running.
 
1 - 14 of 14 Posts
Top