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Old 11-07-2014, 10:39 PM   #1
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Exclamation Intermittent charging system problem

i have another problem to resolve with my 2005 high mileage malibu LS v6.
Three times it has shut down on the road,with abs warning, then loss of power steering, then lockdown to 5mph,then stop engine,all happening over about 10 seconds. On each occasion, the battery was dead. The dealer'* very experienced mechanic narrowed it down to computer shutdown due to no electric power. This seems very reasonable. The dealer tested the battery, told me to replace it, and I did, with a new one. It has done the same thing twice since that. A voltmeter plugged in to the cig. lighter shows its charging intermittently,whn I get above 12 volts, it stops charging often. Sometimes shutting off the engine fixes it for a short while.it never makes it to 14 volts.
I tested the voltage at the alternator, same as at the + battery terminal.there is only one other wire to the alternator, I can't find out whether it is a field wire,or a signaling wire to turn on the alternator. It has about 4.5 volts dc on it when ign on and car running. I connected an oscilloscope, and there is no ac or digital signal evident,and the only other thing seen is a bit of ignition hash picked up from the nearby distributor.. I currently have a brand new alternator installed, with absolutely no improvement.
I need to know where this small wire comes from, and what kind of signal it should have. I want to check continuity of the wire. Could it be a problem with the computer? The only code stored after one of the three shutdowns was lean condition, probably irrelevant.
Does anyone know where to look next? I am putting on a new serpentine belt next.its quite old, but I don't think it'* slipping.

Last edited by Ralph Lewis; 11-07-2014 at 10:43 PM. Reason: found a misspelled word
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Old 11-08-2014, 09:48 AM   #2
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i am looking at the diagrams and that is the only wire and it is supposed to have 5v so seems fine. make sure your belt is good and the engine grounds are good. maybe compare the voltage to another 5v source see if they are all 4.5
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Old 11-08-2014, 12:22 PM   #3
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Exclamation Intermittent charging problem malibu 6cyl

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Originally Posted by jwfirebird View Post
i am looking at the diagrams and that is the only wire and it is supposed to have 5v so seems fine. make sure your belt is good and the engine grounds are good. maybe compare the voltage to another 5v source see if they are all 4.5
i checked with voltmeter, and I have 5 volts when it should be charging, so computer probably ok.
Then, I found another post about another charging problem, which described a fusible link between alternstor and battery positive. Unfortunately for me,the car was charging pretty well this am. As soon as I put it into reverse to take it for a run,the charging stopped abruptly. I followed the advice in the other post, and connected a jumper cable from the battery positive to the alternator outpot, and voila! Charging to 13.5 volts on the meter immediately. There is something intermittent between the alternator output and the battery. Possibly the fusible link partly melted, and the snap of shifting gears separated it. We did have an accidental short circuit briefly when reconnecting the wiring after a recent transmission swap on the same car, so I suspect a wire is fried. At least now there is a way of fixing it! In fact, when the jumper was applied, the partially discharged battery loaded the alternator so much that the serpentine belt began to slip a little. I'm out this am for a new belt, and I have to look for the interruption in my cable, and repair or replace.
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Old 11-08-2014, 02:13 PM   #4
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Definitely your problem, the alt on your car is only on or off signal from the pcm so it has to see the battery charge through that cable, if it is intermittent so is the charging. The fusible link is just a little bit of thin wire that provides a safe place to pop. Could be half blown or poorly conducting. Could be the terminal on the alt or stud or cable ends need cleaned
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Old 11-09-2014, 01:20 AM   #5
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Definitely your problem, the alt on your car is only on or off signal from the pcm so it has to see the battery charge through that cable, if it is intermittent so is the charging. The fusible link is just a little bit of thin wire that provides a safe place to pop. Could be half blown or poorly conducting. Could be the terminal on the alt or stud or cable ends need cleaned
Resolved the problem. The terminals and attachments all are ok, so I replaced the bad wire with a new fused link to the battery positive. Car charges to 13.7 volts even at fast idle. Your assistance with verifying the proper voltage on the wire from the pcm allowed me to take the next step.
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Old 11-10-2014, 08:09 AM   #6
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thanks for updating your fix
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