My daughter drives the old 2002 dakota 2wd AT 4.7l v8. The check guages light came on, and the voltage gauge was way down. Battery tested around 11 volts, the alternator wasn't charging. Its got about 195k on it so I replaced the alternator before doing much investigation. Well, it still doesn't charge with the new alternator on it.

Stuff that's not my problem:
Voltage at the top of the alternator is about the same as at the battery, around 11.8 with the engine running, so the alternator is not activating).
No fuses are labeled alternator, but I checked anything that sounded remotely related (i.e. not "power windows" and stuff like that, but I checked the rest).
The battery temp sensor tests around 3.5 K-ohms at 93 degrees. According to one source for all temp sensors, that might be out of spec. Can anyone confirm or deny that?
The green wire going to the alternator (which the ECU is supposed to ground to activate it the alternator) is grounded. So I think the ECU is trying to activate the alternator...?

The white wire which is supposed to be powered is not. With the engine running, if I apply power to the white wire the alternator starts working. Voltage comes up from around 11.8 to mid-high 13s like its supposed to.

From my googling, I had gotten the impression the white wire should always be powered and the ECU pulls the green wire to ground to activate the alternator. Is this right? Is there any reason why the white wire would not be powered, other than a wiring harness issue?
Does anyone know off hand where the other end of the white wire is? so I can check if its powered at the other end?

Thanks,
Joe

 

Check and clean all your grounds + battery terminals. Check your cables and make sure corrosion hasn't crept up into the insulator. Use dielectric grease on everything.
Take the new alternator back to the store and have it tested. Won't be the first time one was bad out the box. The voltage regulator is a part of the PCM.

 

So I found this doc, which says Chrysler has used both A and B side regulation on their alternators. Previously I was getting the impression the reluation activity should on the ground wire not the positive. But if the regulation is on the positive, that means it could be the PCM deciding to not activate the alternator....

Does anyone know for sure if the 02 Dakota uses A side or B side regulation on the alternator?

 

It's not set up quite as the doc but it's A. Ground side switched.

Power is supplied from the PCM via the generator source output to one of the field terminals. This source also supplies the leak detection pump and on some models, the transmission control relay.
The ground is sinked via the PCM generator field terminal.

You are correct, the white wire should be "hot." It's not uncommon for the PCM to fail. The voltage regulator is internal.
Are you showing any codes? There is also the battery temp sensor that can limit the charging rate.

 

So... If the leak detection pump or transmission control relay was defective, could that cause the white wire to not be powered?
I'm trying to figure out if its definitely the PCM, or if there are other things I should check first

Its showing P1495, which I think is unrelated.
The battery temp sensor measured 3.5 K-ohms at 93 degrees. But I don't know if that's good or bad.

Thanks for your help!

 

It's probably related.

P1495 - an open or shorted condition detected in the Leak Detection Pump circuit.

You might disconnect the LDP first and see if you're charging.

 

I was out of town for a week, I'm back now.

Even though I didn't think it was the culpret, I ordered a battery temp sensor because its around $12 from RockAuto. It just felt like wasting the $12 was a good idea before spending nearly $200 on a computer. It didn't help.

I think I found the leak detection pump. Unplugging it doesn't change anything. I think next up is ordering a ECU.

Is there a place you guys have had good (or bad) luck with on ECUs? I'm leaning towards Flagship One. They're not the cheapest, but they have a lifetime warranty and no core charge.

 

I ordered from Flagship One. They feel a bit sketchy, but I ordered anyway.

Sketchy thing # 1:
I started with a chat, asking if they help diagnose to confirm the ECU is the cause of the problem. She asked what symptoms I'm having.
I typed a short paragraph. 1-2 seconds later (no where near enough time to read, consider, and select a reply) she replies saying that is usually the ECU, but it could be something else, so they recommend having a local technition test it it first. Then followed up with 90% of the time its the ECU.
But that first reply came far too fast to have actually read the symptoms. Feels like copy and paste from a script.

Sketchy thing #2:
So then we're on the phone ordering it. When chatting with her, I said I have a Dakota (because the same part # is used in the RAM). Part way through the call, she tries to confirm I have a RAM. She says she thought I said RAM, the one for the Dakota is about $50 more. I tell her I'm looking at the price on their website, and its the same for both - $179.99. She puts me back on hold then comes back and agrees to that price. On their website there is no price difference. It feels like she just wanted an extra $50.

We'll see how this goes...

 

All PCM reprogrammers are sketchy. If you knew how that side of the business worked....

 

I can imagine.