Battery Charge light on, system is charging

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gixer2000

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I had the exact same problem on my 07 and it was a broken wire from the alternator to the pcm. I never actually found where it broke but with a diagram and a DMM I was able to do a continuity test on the wiring. Instead of finding the broken wire I ran a new one, soldered and shrink tube the connections then tucked it into the wire loom.
 

rjdelp7

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I had a red Alt light on an old Chevy. The Alternator was overcharging and battery went soon after. Just because its charging, does not mean its correct. The car runs off battery and alternator maintains voltage. The alternator must charge its field coil, so it needs steady 12.0v from the battery. It may be a bad connection or ground.
 

Don_Muddiman

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I had the same problem 6 months ago. I spent many hours diagnosing the problem, even replacing the alternator. It ended being the three pin pigtail that connects to the alternator. The pigtail pins are B+, GENMON and GENCOM. The GENMON pin ended up having a bad connection causing the PCM to not read the alternator voltage. I purchased a new pigtail from Advance Autozone, cut the old one off and solder the new one on. Try pressing and tugging on the connector while monitoring the PCM Body Control Module or the alternator light. You'll need a ScanTool 426101 OBDLink MX Bluetooth and the FORSan software to really see what's going on.
Don
 
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rray

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Mr. Sticker, Thank you for the information you posted. I agree with the swapping out of parts. However, I had already ordered the Fusible link and changed out the Alternator. Neither one of those items fixed the problem. I've cleaned all the electrical connections I could get to. No luck. It seems that as soon as the key is in the on position, and the dash does it's self test (lights come on then go off) as soon as the key is put to the on position, the BATTERY charging light is on. This is different from the video above, where after the car is running for a few seconds, the charging light then comes on. From the video above, I need to check the 3rd wire, to see if there is a field response back to the PCM. I'm guessing there is since my light is always on. I will check that out this afternoon and post again on the outcome. Thank you!!
 
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rray

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Don_Muddiman: I've since changed out the 3 fusible link, which is the connection to the alternator. The 3 pins. Mr. Sticker shared a video where the mech tests the 3 pins. I'm going to try that next. At least for voltage at this point. Thank you for the information. I'll keep posting till I find a fix.
 

stamp11127

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The alternator is now controlled by the pcm. The communication between them is referred to as "pwm - pulse width modulation". Think of it as the amount of "on time" compared to "off time" per second expressed in percentage. Each second is divided into 10 equal units of time. A duty cycle of 50% will have a signal at 5 of the 10 units of time. We are now talking digital signals between the two components. The only tool that can "see" those signals is an oscilloscope - your voltmeter(dmm) doesn't respond fast enough to provide accurate results, if any. The only use for the voltmeter is checking continuity of the harness between the alt and pcm.
 
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rray

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Stamp11127. Off to Oscilloscope land I go.. I think the DIY garage on base may have an Oscilloscope. I'll head there this week to find out. Thanks again for the info.
 
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rray

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Don Hall> I've replaced that wiring harness. It is the fusible link from the alternator to the battery. No luck. My light comes on as soon as the key is turned to the on position. Then stay on while the engine is running. All volts to and from the battery and alternator are normal. New alt and new wiring harness.
 
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