2004 KJ Charging issue (revisited again)

Hi All! I have read in other posts about KJ Charging problems so here is mine...My 04 KJ has had the original alternator since the day I drove her off the showroom floor and she has never had any electrical issues ever! Last week that changed. I was on my way to work and the battery light popped on by the time I got to work the battery was dead. The battery is less than a year old and so I charged it up load tested it and it is good. Checked the alternator and no output so figured no big deal 17 years was a good run for the original and figured time to upgrade to a 160 amp unit. Got new alternator installed and surprise light still on! Check alternator again no output. Changed battery temp sensor and light still on! Ran a wire test to see if fusible link blew and it's still good. Exchanged the alternator and still no output. I have read on the forum that the pcm commonly goes weird and that people have wired an external regulator instead of getting a new pcm. Would the external regulator be the better option. I did sort through the wiring and found no breaks. Thank for listening!

What brand of alternator have you installed? Did you get it bench tested for good output?
We have heard of aftermarket Alts out of the box dead. OEM alts /Denso are best & do last a very long time!
HJ got a 136 one out of the bone yard that still works today.
Bill our electrical specialist will chime in to assist further re the PCM potential issue, with further information.
See this post as well: https://www.jeepkj.com/threads/replace-alternator-or-repair-it-kj.76170/

I agree that OEM/Denso are the only way to go and need to be bench tested.

I have a bit of a problem in that the 2004 Service Manuals are difficult to get hold of so I have to alternate between 2003 and 2005 models to try work things out in the Wiring Diagrams.

Do not concern yourself too much about the Battery Red Light coming ON..this can happen even when the Alternator is charging well...measure the charging voltage across the Battery..should be around 13.4 Volts.

Make sure your Battery Terminals are very clean and tight.

The Negative lead going to the Chassis must be clean and tight both ends and the two Engine Grounding Straps at the rear of each head must be clean and tight all ends.

What did you do with your original Alternator ....if you still have it maybe some new Brushes and cleaning of the Brass Commutator Ring may fix it.

How did you test that the Fusable Link is OK? Disconnect the Battery completely and measure the Link end to end for continuity.

My Export 2002 CRD still has the original Denso Alternator...only problem I had was the Battery Light coming ON due to the Temp. Sensor having no ground on one end. The Temp Sensor in any case does not change the charging much hence the reason why it was not fitted from 2005 onwards...although the Manuals still refer to them!

Take a thick cable such as a Jumper Lead and clamp one end on the Negative Battery Terminal and the other end onto the Alternator Casing and see if the output now becomes 13.4 Volts...this will prove if all your Grounds are in fact good!

Re-plug the PCM Connectors a few times ....with Battery dis-connected..in case of a dirty contact!

Swap over the ASD Relay with an identical one nearby.

Check Fuses # 6 and 26 in the PDC.

First Update! The alternator that I got was an Ultima 160 amp from O'REILLY'S new not reman. On a whim I took it back to them and had them bench test it and to both our surprise the alternator had a bad regulator on it so they ordered another one for me.


Update 2 Got the replacement alternator same brand and specs as the first one and got it put on only to discover that the battery wire terminal was crushed as it had been dropped. I bent it back straight knowing it was probably not going to work and it didn't. So now I am waiting on the third alternator from O' Reilly's. And yes I still have the original Denso not planning on giving it to them. I beginning to think the series of bad alternators is the whole problem! Will keep everyone posted

Update 3. This is becoming quite frustrating!! 4 Alternators later, a battery load test, ripping through the wiring, checking every wire for continuity, checking and testing fuses and relays and still NO CHARGE! I am now down to the PCM as suspect. My jeep starts and runs great no issues that way....the only thing I have not done yet and I found this on another post was to ground the alternator and force the field on..

The alternator is grounded in any case by being bolted to the engine but no harm in adding grounds.

Have you checked the grounds from Battery Negative to Chassis and the two grounding straps going from the rear of the heads to the Firewall?

Not having Wiring diagrams for the 2004 KJ is a big problem....the 2003 charging diagrams are completely different to the 2005 diagrams!

Can you tell me what wires are coming off the small plug on the Alternator.

Is it one wire or 2 wires?

The 2003 KJ has a WH/DB wire ie. White with Dark Blue Stripe and a solid Dark Green wire while the 2005 KJ has a BR/DG ie. a Brown wire with a Dark Green Stripe and a Black wire going straight to Ground at G111. If you have a solid Black wire this should definitely go to Ground!

What are the wire colors on your 2004 KJ Alternator?...usually a dominant color with a stripe ie. DB/WH means a predominate Dark Blue with a White Stripe.

This would help me decide whether to try the 2003 or 2005 wiring diagram.

Maybe the Battery Temperature Sensor is a problem although usually it only has a slight effect on charging.

You can lift the battery and pull out the Battery Temperature Sensor, measure its resistance at room temperature and then measure the resistance while heating the Sensor up with a hair-dryer or place it on an incandescent light bulb...resistance should change as it heats up!

One side of the Bat Temp Sensor should go to ground...usually a solid Black wire. If ground is not there on one side of the Sensor...add your own to chassis .....I had this problem!

Are you 100% sure the Fusable Link has not blown...very easy to blow it while swapping out Alternators!

This is the thick wire going from the large connector on the Alternator to the positive terminal of the battery.

Disconnect the battery completely...very easy to blow the Fusable link while working on it with power ON.

Remove the Fusable Link from the large stud on the Alternator.

Measure the Fusable Link from end-to-end for continuity with your Multimeter.

Final update....After all the time and effort trying to figure this problem out I gave up and sent the jeep to a shop in hopes they had better luck than I had. Well after over a week they finally found the gremlin! Turns out it was a single wire in the harness going into the firewall that somehow came loose in the connector and no longer making contact. They suspect that one of 2 things may have happened. 1. A rodent may have been trying to chew on the wires and pulled it loose or 2. Because I have a 3" lift on my KJ and the suspension rides like a buckboard that it got rattled loose from banging around. Whichever it was I am just glad it is fixed and back on the road!