OT:06 Chevy 2500 not charging

redtom · Jan 9, 2015

At work we have a 2500 HD, 6.0 gas. Not charging. Loads of miles so I put on new alt. Not charging still. I find no 12v power at either of the 2 little wires at alt. This unit has been jumped a lot of times since the key gets left on a lot (switch is janky). It is a security vehicle that gets stopped and started dozens of times 24 hours a day, so switch wore out. I ordered a new switch today. Any tips

Steve@Advance · Jan 9, 2015

Is there power to the big output terminal? If not the fuse or fuse link or the wire itself is burned out. Especially if it's been jumped off a lot. Not good for the alt or wiring to try to bring a dead battery up.

There also needs to be power to the other 2 smaller wires when the ign is on.

redtom · Jan 9, 2015

Both the little wires need power?

Richard G. · Jan 9, 2015

Make sure you get the larger alternator that puts out more amps. We were in KY last year and the 2500 truck quit charging. A local mechanic came and charged the battery and we went to his shop. Took the alternator to a parts house and got a replacement and it quit in less than a mile. Took it back and went to another parts house and they said the alternator was not the correct one. Got the higher amp and made it home the next day with no more problems. The shop only charged us $80 bucks for all their work and ferried us to and from a motel 11 miles twice. It was late Saturday when it failed the first time.
Richard in NW SC

Steve@Advance · Jan 9, 2015

Yes, the small wires need to have power. The S terminal will be hot all the time. The F or L terminal (depending how it's wired) will be hot with the ignition on.

4play · Jan 9, 2015

(quoted from post at 23:43:51 01/09/15) Yes, the small wires need to have power. The S terminal will be hot all the time. The F or L terminal (depending how it's wired) will be hot with the ignition on.

No, the small wires go directly to the PCM. The S terminal is not even used. The engine computer controls of the charging system on these trucks. The two little wires are "F" (gray) and "L" (brown). The PCM uses a duty cycle on the field circuit to control output. The "L" circuit is simply for charge indicator.

Sadly a lot of vehicles have moved to PCM controlled alternators some for a long time, it sure complicates matters when trying to decide if the PCM could be the problem or not. Diagnosis should include testing the PCM for codes and tracing wires from alt to pcm, but more than likely its the alternator that is the problem, as easy as it is to remove I would have them double check it. After that its time to test wiring.

Owen Aaland · Jan 10, 2015

Make sure the alternator is the correct one for the vehicle. The older alternator looks the same as the newer one that is PCM controlled but they use different regulators.

gab · Jan 10, 2015

Like already stated I think the small wires go to the pcm, however a good place to check for any electrical problem is under the big electrical center on the left inner fender, that's a mouse magnet, don't make any difference if it's stored in a corn crib overnight or a brand new fancy garage.

OT:06 Chevy 2500 not charging

redtom

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Steve@Advance

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redtom

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Richard G.

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Steve@Advance

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4play

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Owen Aaland

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gab

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