My overcharging saga

[DanByrd2]

Long time lurker, first time poster. Bear with me fellas. 

 

I purchased a 2002 with a flatbed for 3k (thought I was getting a decent deal) with wore out tires, an overcharging problem and a relatively bad oil leak. I knew I was going to have to dump some coin into the truck but now the frustration is getting to me.

 

The first weeks I had the truck I didn't do much besides clean it, the guy I bought it from abused the truck to death and didn't fix much of anything. The guy would unplug the alternator, drive to work, plug the alternator in at lunch and let it charge for a bit and then unplug it and drive home. Who knows how long he did this for. 

 

Cue me.

 

I did t think much of the overcharging problem, figured it would just take a new alternator and I'd be done with it... hah! The alternator on it was supposedly new, I had it tested by Napa and it passed with flying colors. I put it back in. So then I start digging... I find that every fuse under the hood is the wrong size, the 140 alternator fuse is jumped with a metal piece, and every bulb in the cab is blown. *this is when I seriously questioned my purchase*... No biggie, my buddy is a certified GM mechanic, I ask him for advice, he says check batteries first and foremost. So... batteries were beyond shot, I replaced both of them and of course nothing was cured. So... I get impatient and research the problem, which leads me to PCM issues. Me and my infinite wisdom decide to buy a used PCM, my thought being I would take it to a dealership and have it reprogrammed. *cue my impatience again* 

 

One day after work, I get the bright idea to plug in this used PCM and see if it still overcharges... I plug it in and sure enough, it Overcharges. Now I'm getting "no bus" on the dash. I plug the original PCM back in, now I'm getting "no bus" on that one too. FML. As the frustration mounted I decided to leave it alone for a while. 

 

A few weeks later I decide I'm gonna take it to the dealership, but first it needs tires. The mechanic my company uses sells tires and will cut me a deal, so of course I limp it over there. I began telling him about everything and he starts to try n diagnose it for me. He S getting no signal from either PCM, and neither of them are charging... he turns me onto NPC out of Houston for a new PCM. I figure sweet, he knows what he's talking about, I'll do that.

 

700 dollars and 48 hours later, I have a vin matched, brand spanking new PCM. I disconnect the batteries, plug it in, connect the batteries and fire it up... I let it idle a minute or so and it doesn't overcharge. Hell yea it's fixed... nope. Today I decided I'd take it to pick up my son from school, I get around the block and the volt meter pegs out again. I drove it back home, parked it and hopped in my 99. 

 

*sigh* 

 

What's next guys? Sorry for the lengthy post.

 

I will add that prior to installing the new PCM I did replace all the fuses with new, correct sized fuses. Also, once I plugged in the new one, my "no bus" went away, but I had every other light on the dash on, and with the original PCM I only had the brake light on and the tranny light. 

Edited January 20, 2018 by DanByrd2
Not finished

[Mopar1973Man]

Check the Green wire from the alternator to the PCM if its shorted out to ground it will continue to overcharge. The Blue wire is +12V key hot so the green is variable ground if it shorts to ground its a runaway alternator just like you are experiencing. 

[DanByrd2]

I'll check it out and report back tomorrow. 

[Mopar1973Man]

Here you go... As can see the blue wire is +12V key hot and the green is the variable ground. Charging systems are super simple and these Dodge trucks. 

 

[SilverMoose]

I had this problem on my 01 1/2 ton. Try checking the voltage manually with a DVM. I did that on mine and charging voltage was normal.  It did not happen constantly maybe a handful of times during a year.    I'm not sure if comparing the different vehicles is valid though. 

 

L8tr

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[DanByrd2]

So I haven't traced the wiring yet (too damn cold and windy) but I did borrow a scanner. I got the following codes.

 

P1693 P1698 and after I turned the truck on I got P0602.