OK

I have a 1996 dodge 2500 12 valve, 4x4. About 3 weeks ago my GEN light came on and I noticed my voltage was at 12 volts instead of 14 on the guage. I figured it was one of the batteries so I replaced the oldest and checked the other battery twice at both autozone and orielly's and they showed the battery good. OK I figure it was the alternator, I replaced that but still no go. I later find out that the computer engine controls the alternator's voltage. I get a new computer engine (PCM) and still the same problem...12 volts and the GEN light comes on after about 5 minutes. I took it to a diesel shop so they could look and they could find nothing, they checked all my grounds, the starter, etc... If they took the alternator off of the battery it produced about 33 volts but when it gets hooked into the battery it drops to 12 volts. Any suggestions? When it initally starts it gets up to about 13.3 volts for about 2 seconds and then drops to 12 volts. I also heard that the crank sensor could cause the alternator to not know that the engine isr unning but that does not seem to be the case. Any help would be appreciated becuase I have exhausted all that I know.

Thanks for any replys.

 

I don't want to be a know it all, but if the alternator on a test stand only produces 12 volts, replace it.

 

generally you have to replace batteries in pairs on these trucks. I have seen several cases where this type of problem was cured by replacing both batteries.

 

If it was on a test stand and only showed 12v, time for a new alternator. Once you load it in the truck, it will be below 12v and pulling on the batteries. Coming from a parts store ex-employee.

 

The 136 amp alternator has the power to pull the charge rate up over 13 in a few seconds if the batteries are high enough to start the truck. I ran mine with one battery shorted for a week or so and although the charge rate was a little lower, the slow starting was the only symptom.

 

What about the battery temp sensor under the left battery?

 

that affects the charging voltage less than a volt and only reduces it when the battery gets hot. I have not run mine since 2000, but now of course I run a remote regulator.

 

Did you get it figured out i have this problem.
let me know scott

 

I meant to post this once I got it fixed, but since I didn't do it by myself I didn't want to

Well I ended up having to take it to an electrical shop, the wire running from the PCM to the ASD Relay ended up being the culprit. It had made its way out of the flex tubing and shorted out near the brake boost I believe. IF it would have been a gas vehicle it wouldn't have even started, but becuase of everything being mechanical on the diesel it still ran but the pcm didn't know it was running becuase of that wire so it wouldn't charge the batteries.