Not charging

2005 CHEVROLET 3500
87,000 MILES • 6.6L • V8 • TURBO • 2WD • AUTOMATIC
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CHEVY FLATBED
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Truck is a c4500 Kodiak. It would not let me select that. a few days ago I had to jump start truck in the morning and then about 3 hours later it barely started. Checked batteries all 3 were 9 years old so replaced those but after it was only charging around 12 to 12.5 volts for 2 days. then the transmission lost reverse then the gauges went out then the sputtered for a minute and shut off. Went back about an hour later fired right up still no gauges ran for about 3 to 4 minutes then shut off again. replaced alternator figured that's what it was started up gauges came on power probe and battery gauges started at 9 volts. idled about 8 minutes then shut off and wouldn't start. have no idea where to start, any tips would help. thankyou
Sep 25, 2020 at 6:33 PM
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JACOBANDNICKOLAS
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Hi,

I have virtually no info on the truck listed. However, I'll try my best to help.

Have you checked body and frame grounds? I know there were issues with the 4500 tiltmaster having faulty grounds to the frame/engine. Also, are you getting power to the alternator? Have you checked fusible links/fuses?

Let me know.

Joe
Sep 25, 2020 at 8:34 PM
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CHEVY FLATBED
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Have not checked any grounds or fuses yet, but the 3 plug terminal going to the alternator has a ground a 12.5 volt and a 7.5 volt or whatever the truck is currently running at.
Sep 25, 2020 at 10:31 PM
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JACOBANDNICKOLAS
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Okay, if you have ground and 12v going to the alternator, it sounds like the alternator itself is bad. Have you had it bench tested? Also, can you upload a pic of it so I can have a better understanding of what you are dealing with?

Let me know.
Joe
Sep 26, 2020 at 4:57 PM
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CHEVY FLATBED
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Have not tested the alternator yet, but it is brand new.
Sep 26, 2020 at 5:09 PM
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JACOBANDNICKOLAS
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I totally understand. However, you can still get one that is bad. I just replaced a new master cylinder today that was new yesterday. Ugh!!! They don't make things like the used to. If you have ground and the alternator is getting power, it should be producing.

You could do it at home without replacing the alt. If you have a multi meter or volt meter, that is all you need. Compare the voltage at the battery with the engine off and then with it running.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

It would be better to bench test it, but this could tell us something as well.

Joe
Sep 26, 2020 at 6:22 PM
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JAMIE RENWICK
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Different man, same issue! Alternator tested fine, I tested the 12v bat wire to the alternator and to the junction box, and it was a perfect 0.0ohm, the junction box to the battery’s is a 0.0ohm, the engine ground strap 0.3ohms
Sep 19, 2023 at 7:21 PM
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JACOBANDNICKOLAS
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Hi,

I attached the wiring schematic for a 3500 below. The 4500 should be similar. If you have power to that alternator, the next thing is the ECM.

The ECM is responsible for the duty cycle of the alternator. The duty cycle of a vehicle's alternator reflects the percentage of time it operates at various levels of electrical output, since we know the alternator is good and it has power, this is the next suspect.

In this case, I would recommend using a live data scan tool to check the duty cycle and for diagnostic trouble codes.

I attached the schematics below. Note that these were made with one or two alternators, so you will notice both in the schematic.

Take care,

Joe

See pics below.
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Sep 21, 2023 at 5:44 PM