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2008 suburban ltz lights dimming and ac fan slowing down at idle

Old September 2nd, 2023 | 9:53 AM
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Default 2008 suburban ltz lights dimming and ac fan slowing down at idle

So I just bought this vehicle not long ago, as I have a big family. The lights all around the vehicle, and the ac fan slows down and dim at idle and when not on the gas. As well as the battery light coming off and on. I've had the charging system and battery tested at the local advance auto and everything checks out. I've replaced the main maxifuse and cleaned and tightened all battery connections, as well as from battery to alternator and from battery to fire wall and everything on between. But it has not fixed the issue.
Old September 2nd, 2023 | 10:00 AM
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Read the voltage across the battery terminals with engine at idle when this happens; I suspect no charging at low/idle, even if higher rpm shows charging.

Did you remove and clean all the negative cable ground connections, like with steel wool and then re-connect? Similar with all the positive connections. Obviously, do all that with battery disconnected. If all good, and still no charging, I'd suspect the alternator.
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Old September 2nd, 2023 | 10:12 AM
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I have cleaned all positive, negative, and ground terminals. I wasn't too sure if it was the maxifuse (not too sure why it's even there cause cars have been running perfectly fine without it for 100 years) or the alternator. So I went with replacing the maxifuse first. But the battery is fully charged as I have checked it with my multimeter as well as the alternator is charging. Checked I with same multimeter.
Old September 2nd, 2023 | 10:20 AM
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Originally Posted by Paulp82
the battery is fully charged as I have checked it with my multimeter
Have the battery checked under LOAD, like somewhere with equipment more sophisticated than a multimeter.


Originally Posted by Paulp82
the alternator is charging. Checked I with same multimeter.
Is it charging at IDLE though ???? Did you test at idle when the other stuff was not functioning correctly? Battery/charge light coming on at low/idle sure sounds like no charging at idle/low speed.
Old September 2nd, 2023 | 10:28 AM
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if it tests ok and you find no problems with the battery and alternator; maybe the dealer has a programming flash to increase charging output at idle.
Old September 2nd, 2023 | 10:47 AM
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I don't think I have checked it while the battery light is on. It's a very intermittent thing and I might have to catch it while it's on.
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