Twice in three days, while driving my '99, the "Check Gauges" indicator lit up. I saw my voltmeter peg to the left, or 9VDC (because it can't go to 0VDC). It normally indicates straight up the middle at ~14VDC. The Jeep keeps running and driving without hesitation or stumble when this occurs. An external voltmeter connected to the battery posts with engine running, e-brake set, shifter in D and electrical system under normal typical load conditions (running lamps lit, radio on and vent blower on #2) indicates ~13.5VDC and the gauge diagnostic functions perfectly. I pulled and cleaned the connectors to the ECM after the first incident and everything appeared to return to normal - until today's event. I need one of you gurus out there to give me a couple of hints as to what to check next. Note that I own a factory manual and I understand the electrical schema so don't be afraid to talk tech with me. At this point I'm beginning to fear the potential loss of my ECM. What say you, oh-wiser-than-me CF Veterans?

 

Happens to me every couple months. My issue is with mud and crappy breaks loose in the alt. I keep a big wrench in the back and give it a couple love taps and it fixes it. Probably not your issue, but works for me

 

My guess is your alt will soon need some brushes...or replacement...just my experience with my 98, acted weird for awhile untill the alt finally gave up.

 

That's in the normal range. I don't think you necessarily have an alternator problem but a gauge problem. Have you checked the cluster connector on the instrument panel?

 

Gents, These are all valid replies and I appreciate your feedback.

I did the "love-tap" and "wire-jiggles" at the alternator but cannot yet be sure that had any effect.

The alternator is suspected as being intermittent as it is original with 183K miles and countless hours of run-time. Could the ECM react quickly enough to sample-and-hold an intermittent alternator voltage "drop-out" then force the voltmeter to indicate 12V or less until reset?

I will check the cluster connector but I doubt that is the case since all else displays properly and passes gauge cluster test (i.e., hold odo reset until beep when keyed on). As you know, all gauges are driven via a two wire data bus so if one wire connection fails then the dreaded "data" (I think) error word appears in the odometer display window.

 

Ah, right. I forgot that yours has that already. I'm curious where the voltage sample for the gauge comes from now. CCD bus stuff is CCKen's neighborhood, I don't know much about it.
It might be interesting to wire up a DVM to your electrical system and go for a drive, to see if it drops low like the dash gauge does.

 

That low voltage indication returned yesterday along with the "Check Gauges" lamp. I responded as soon as it appeared and pulled over, shut down, popped the hood and cycled the PCM connectors but to no avail - the gauge indication didn't change following restart. The voltmeter gauge went to "practical zero" during the (thankfully) short ride home. Once in my garage, with engine running I gently rapped on the alternator housing a few times with a long steel rod and then the voltmeter gauge registered mid-scale (~14V). I think this response to tapping the alternator combined with the tips from xjfirefighter and captainwoot are steering me towards alternator service (thank you very much). I think I can obtain a set of brushes or perhaps a rebuild kit/procedure from a local rebuilder but time is short and there are plenty of things to do before I start commuting for a new job this Monday. It always comes down to the old "spend the time or the money" dilemma and right now I feel I have neither...

Question: What to do? Replace alternator outright but at what cost or just pluck it and rebuild it with whole day lost? (Hey! I rhymed!)

 

Here's a pic of the brushes removed from the alternator. Not too bad a job to do. Two hours of my labor, a little time out for lunch, some run-around time and forty dollars for a quickie rebuild. Started the job before noon and was back up and running by ~3PM. Just look at the original brushes that came out - I'm impressed that they held up as long as they did (183K miles and countless hours run-time).

 

Can you give us the name and part number of the rebuild kit you used? I have a spare alternator I'm going to bench rebuild "just in case".

 

Sorry, no. I ran my alternator over to the auto-electrical rebuilder in a neighboring town. That's why it cost $40 instead of $20. I'll call him for a Manufacturer and P/N then post it here.

 

I called the folks at Auto Electric Supply in Hyde Park, MA. The person on the other end of the phone indicated their part manufacturer is "WAI" (which stands for World Auto International) and the the WAI part number to replace the old brushes in the picture is #39-8206. I asked about a "kit" but he said they don't buy them in kit form, only piece parts for popular brands.

They sounded busy and may have been just blowing me off, so research the info before you spread the word or order parts for yourself. I really hope he wasn't just whistling dixie.