Electrical failure UNLIKE other posts

2004 Montana. 167,000 miles. Until now, only replaced tires and thermostat. Battery light randomly on and off for 3 month's. Lights never dim, ALWAYS charging. Monitored voltage for 2 weeks at cigar lighter with digital voltmeter. NEVER below 13.65 volts when running.

Varied between 13.65 and 14.9 volts. Light appears when voltage is less than 14.2 volts, but light off voltage seems to be above 14.3 volts.

Again, no other indication of problem except for battery light on. No dim lights ever, no hard starts EVER. Even at 20 below zero, engine spun right over and started.

Took 2000 mile trip last weekend. Left North Dakota, headed to Texas. Van ran perfect, and when outside temp was above 32 degrees: no light. Upon return (8 miles from home), battery light came on, headlights dimmed, heater fan slowed. 3 blocks from home, all gauges died, engine sputtered, eventually died and car was electrically dead. EXCEPT the dome lights were fine.

Tow vehicle arrived 10 minutes later. Turned key to put van in neutral for the tow, and dash lit up. Turned key to start and van started, gauges worked like normal, drove it home. Headlights bright.

Next day, van starts as normal (warmed it up 10 minutes) but when put into gear to drive, it went 4 feet and died. still dead. I get a relay click in the underhood fuse box when key turned on, but otherwise dead. Battery still rock solid.

Any ideas?
Thanks

Any Auto parts store can do a free load test on both the battery + alternator.
Do a good visual inspection and check for loose battery connections.
How old is the battery?
If > 4-years old , it's time for a new battery, a tow service bill could of covered a new battery!

Also look for bad grounds/ battery connections, take them off clean them look close as mentioned, at all connections.

I am POSITIVE problem is NOT Battery. Pretty sure NOT Alternator.

Battery static voltage never below 12.6 volts as measured at cigar lighter. Battery is less than year old Interstate Megatron.

While battery light on, I have run everything on this van full blast simultaneously including trailer lights and the lights never dimmed, or fan slowed down. 3 month's of this intermittant battery light and never a hint of any other symptom, so I can't believe alternator is problem. This has gone on for approx 8000 miles.

NOW, it finally died at the end of our trip. Battery is still fully charged, but the dash is dead. Dome lights still bright. Battery strong. Alternator no factor when engine not running.

Another weird tidbit is that when headlights dimmed at the end of our trip, I started shedding electrical load to preserve battery power. I turned aftermarket stereo off, but the face lights stayed on (it does that). The weird part is that even though everything else was dead, the stereo light and dome light were fine, although everything else was dead.

Not sure which one it is, but a centrally located (shorter than the rest) relay in under hood fuse box clicks when key turned to on. It was dark when I checked this. I will troubleshoot more now that I have daylight.

Thanks for the reply, got anything else? ANYONE??

Took to dealer last week before big trip and he said he has no idea, he would have to tear the car apart looking for possibilities...hundreds of dollars of troubleshooting to maybe find nothing. I am sure they could find it now as it is hard broke..finally. Just glad it made it 2 blocks from home before it quit! It has been a FANTASTIC car.

I will check, clean and re-make all connections from battery to engine/frame. Also check for voltage drop on any connections before and after this tasking.

I have had no complaints about this vehicle as it has been a fantastic trooper for us, but the charging system is weird that it has like 7 modes of operation, but no way to check to see if these "modes" are doing what they are supposed to do WHEN they are supposed to be doing it. I have thought all along my problem was a bus issue where the alternator was in one mode when the system THINKS it should have been in another.

NOW, I have a hard break where car is dead. Dome light works, and stereo light on when everything else is dead. How do I get 12 volts do stereo and dome light, but everything else seems to have none? Door locks dead too. Funny story: My Norwegian wife was "locked-in" the car when it died 4 feet from where she put it into drive this morning. "I can't get out! The unlock button does nothing."

I pointed and laughed...then told her she could manually unlock the door.

I will troubleshoot further and post my findings.
Thanks for all the help...

Turn key to "on", don't start......you may have more than one fuse block on this vehicle(underhood, interior).....check for power to the fuses with a test light.....if you have a some with power and some without, check the output legs of your ignition switch....

Could also have a wiring problem at the underhood fuseblock.....it may have "silver" colored locking bolts on top between the fuses/relays.....make sure they are tight......

Thanks Tech II. I will check those things you mention. Will post results.

Only test's can rule out the battery + alternator!

A bad Body Control Module (BCM), or a bad relay going to the BCM can cause flaky auto body electrical issues.

-or-

Dirty, burnt, or worn contacts on the Passlock system (ignition switch) could give a false signal to the BCM.


Tests:
Roll BCM/Relay with another the same type.
Battery/Alternator Load test
Fixing Battery drain test - http://www.youtube.com/watch?v=B__DqK90IIc

Daniel,

I suspect a bad BCM, or whatever powers it, or distributes from it.

But, just to be sure, I removed battery and am taking in for testing.

Talked to local parts store guy who blames alternator, but if it weren't charging, I would have had dim lights all along...or at least a time or two...and battery would have gone dead long ago in this cold weather.

Stay tuned!!

O.K., Battery was dead. Brought it back to Interstate, they will charge and load test. Still thinking battery is good. He gave me a loaner. Brought it in for load test. Turns out, it is currently NOT charging. 12.5 volts engine off...11.7 engine on. RPM no factor in voltage. NOW looking like alternator issue.

HOWEVER, battery light still off and on. Voltage steady at 11.6/11.7 engine running, but battery light intermittant. How is battery light intermittant when voltage steadily below 12 volts?

Next step, r/r alternator. NOT looking forward to this in the wind and snow. I hope that is my problem, because I would HATE to do this hateful job only to find out it was something else!!

probably not an issue here, but the belt tensioner died and my van wasn't going anywhere. It was made out of plastic!!

Alternator did fail at the tail end. Replaced, charges now. Thought problem was solved. I am right back whre I started. Charges fine. Replaced alternator two weeks ago, charging like normal, with normal voltage. Only problem: Battery light on in random fashion. Exactly what I started with.

Dealer has no clue. His only solution is to charge me hundreds of dollars to explore connections and such...

Dealer has no clue? If a GM dealer, then go to another one......

BAT light should not come on when voltage drops below 14.2 volts.....

Are there any IPC codes, or "U"(communication) codes?

Need to read serial data to PCM and also to IPC....a garage with a generic scan tool, probably can't read this....