Alternator not charging

Tiny
ALMNOP
  • MEMBER
  • 1996 DODGE RAM
  • 5.2L
  • V8
  • 4WD
  • AUTOMATIC
The "gen" light on the dash came on a few times randomly. Charged the battery just to be sure. Went to the store a day later in the dark, all was fine. 2 minutes later, I went to leave, and had no headlights, only parking lights. Voltage gauge showed very low voltage. Went home, charged the battery, then started the truck and pulled the positive cable off of the battery, truck died instantly.
Assuming it was the alternator, (the battery is only a few months old) I installed a new one. Charged the battery to full before running and all seemed fine.
Now, two weeks later, same thing tonight. Left to come home in the dark and my heater blower motor didn't work. Figured it went bad. The headlights did work at that time. I just went to leave again and NO headlights, no blower, low voltage again.
Any chance there is something else wrong or did I just get a bum alternator?
Any help would be greatly appreciated.
Sincerely,
Alan W. Stott
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Monday, October 6th, 2014 AT 1:03 AM

41 Replies

Tiny
CARADIODOC
  • EXPERT
Don't disconnect the battery when the car is running it can damage the electronics.

It sounds like you got another bad alternator (cheap) get an ACDelco or you have a wiring issue. Here is a guide to help test the wiring and thwe alternator wiring diagrams below so you can see how it works.

https://www.2carpros.com/articles/how-to-check-wiring

The thinking is that if you disconnect either cable and the engine stays running, the alternator must be working but a lot of them will stop working due to the voltage regulator responding to the dips in the "ripple" voltage being produced. That will make a perfectly good alternator appear to be bad so that test is not valid.

Three things are needed to generate the output current. They are a magnet, (electromagnet, in this case), a coil of wire, and most importantly, movement between them. That's why the belt needs to make it spin. One thing that can save you from doing damage by removing a battery cable is not raising engine speed. Generators are relatively inefficient at low engine speeds and their output voltage is less likely to rise to dangerous levels, . . . as long as you don't raise engine speed.

One other thing to keep in mind is batteries give off explosive hydrogen gas. Regardless if your generator is working or not there is going to be a big spark when you remove a battery cable with the engine running. Either the alternator's current will be recharging the battery, and that can be up to 20 amps, or the battery is going to be supplying the car's electrical systems, and that can easily be over 30 amps. That kind of current is going to create a big spark when a connection is broken or reconnected. Small arc welders run as low as 40 - 60 amps and look at the sparks they create. The reason we don't hear about more battery explosions is because people are careful to not disconnect the cables when there is current flowing through them. It's also why there are huge warning labels on all battery chargers to be sure they are turned off before connecting or disconnecting them from the battery.

The second most common failure is the main suspect when you have what appears to be multiple alternator failures. That is a break in the wire from that second smaller terminal to the voltage regulator inside the Engine Computer. For this you'll find exactly the same voltage on both smaller wires, typically around 12.2 to 12.6 volts. That means the difference in voltage between the two wires is 0.0 volts, and that means no electromagnet is being developed. This is almost always caused by corroded or spread terminals in the connector between the engine and body.

If you do find 4 - 11 volts on one terminal but output voltage is also low, as in 12.2 to 12.6 volts, suspect a defective diode inside the alternator, but those are rarely intermittent. It would be more likely there's a bad connection inside, but that would be really rare.

Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.

Cheers
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+2
Monday, October 6th, 2014 AT 2:06 AM
Tiny
JDBEAULOYE
  • MEMBER
I had this problem as well its was a second bad alternator.
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Friday, November 9th, 2018 AT 5:03 PM
Tiny
CHRISHOY19
  • MEMBER
  • 1996 DODGE RAM
  • 6 CYL
  • 4WD
  • MANUAL
  • 12,300 MILES
My serpentine belt frayed and ripped the wire out of my crank sensor and my battery won't charge, I have thrown parts at it for two weeks. 3 alternators, 1 alternator fuse, 1 asd relay, 1 battery isolator relay, and is still can't get the batteries to charge. I finally found the crank sensor problem after all that and replaced it, but still no charge from the alternator. My tach doesn't work either. I don't know what else to do?
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
RASMATAZ
  • MEMBER
Check fuse no.4 30amp in the PDC if okay and wiring too-Sounds like the problem is coming from the computer field generation driver circuit of the alternator
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
BERNICOT
  • MEMBER
  • 1997 DODGE RAM
  • 340,000 MILES
I blew a rad hose right behind the alternator and I seen my volt guage spike then go to normal, my charging system then stoped working so I installed a new alternator, that didnt work so new battery, that didnt work either, check all fuse's their good! What next?
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
WRENCHTECH
  • EXPERT
Check for power at the main terminal of the alternator with the key OFF. If no power found, check fusible links and maxi fuses. If power found, may have problem with PCM. That is where the voltage regulator is.
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
JDL
  • EXPERT
Any applicable trouble codes? Can you communicate with computer? Did you check the generator fuse in power distribution center?

Use a digital multimeter at bat terminal on generator, what does it read, engine running?
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
BERNICOT
  • MEMBER
I did check the maxi fuses, and no im not able to comunicate with the computer, I dont have access to a code reader, I was able to drive the truck as long as the battery was charged, when the battery dies so does the truck, im going out to check it out with a multi meter
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
BERNICOT
  • MEMBER
So I used a multimeter and found I have battery power to the main terminal on the alternator. Thoughts?
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
JDL
  • EXPERT
I didn't see wrenchtech, when I posted, he was here first. You don't need us both, have a good day.
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
JDL
  • EXPERT
If wrenchtech is out of pocket? You don't need a code reader for some codes. You cycle the ignition switch, turn key just till dash lites come on, no further. Cycle the key, on-off, on--off, on, the the mil on the dash starts flashing, you count the flashes to get the codes. Your looking for two digit codes. Example, a code 34 would be three quick flashes, a slight pause, then four quick flashes, get the picture.
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
WRENCHTECH
  • EXPERT
No problem, I went to lunch.
You can test but you may have a bad PCM.
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
BERNICOT
  • MEMBER
Can I replace my pcm with a used one?
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
WRENCHTECH
  • EXPERT
It has to be reprogrammed to your truck but you first need to positively know that is the problem.
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Friday, November 9th, 2018 AT 5:04 PM (Merged)
Tiny
BERNICOT
  • MEMBER
I checked the code's and got 34 74 1 55?
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Friday, November 9th, 2018 AT 5:05 PM (Merged)
Tiny
JDL
  • EXPERT
No generator codes listed. The two smaller terminals at the generator are field terminals. The white wire with dark blue tracer is source voltage, engine running, shouldn't be less than 10 volts.

If you want to word it this way, the voltage regulator circuity is in the pcm. The second smaller wire, the computer switches that circuit on and off to control charging. Could be wiring issues, could be computer issue.

Make sure the battery has a full charge. A couple of the codes, you listed, I don't know what they are?
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Friday, November 9th, 2018 AT 5:05 PM (Merged)
Tiny
WRENCHTECH
  • EXPERT
If it is the PCM, you can just install an external regulator.
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Friday, November 9th, 2018 AT 5:05 PM (Merged)
Tiny
BERNICOT
  • MEMBER
Thank you all for your help, im gone on holidays so I wont be working on this till next week. Thanks again!
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Friday, November 9th, 2018 AT 5:05 PM (Merged)
Tiny
JDL
  • EXPERT
That external regulator is a good idea.
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Friday, November 9th, 2018 AT 5:05 PM (Merged)
Tiny
BERNICOT
  • MEMBER
The external regulator is an awesome idea! I cant figure out how to wire it properly though, I miss the old days!
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Friday, November 9th, 2018 AT 5:05 PM (Merged)

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