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  #1  
Old 08-05-2011, 06:59 PM
Velocity09 Velocity09 is offline
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Battery good, Alternator Good, gauge shows low voltage.

I have a 2002 4.7 Dak with 118k miles, never replaced anything besides battery and oil changes. Never have had any problems until now. It started with my check gauges light coming on and I noticed my battery gauge went all the way to the L. I made it home turned it off and on and everything seemed fine except my battery gauge was just past the 1/4 mark. Drove it again the next day and it finally died on me. I've researched this problem and all I could find is that, it could be one of three things battery, alternator or pcm. I replaced the alternator and battery but is still doing the same thing. Any other suggestions? What exactly is the PCM? is it the black box with fuses under the hood? Is there a Fuse for the alternator? I checked my connections and were all clean except for this connection to the alternator (i've never posted pics hope this works). I also tried removing the negative cable while it's running to see if it'll stay on, It didn't ( I read mix reactions to doing this since it could mess up the computer).
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  #2  
Old 08-05-2011, 10:19 PM
AandPDan AandPDan is offline
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Did you clean that connection?

The PCM is the Powertrain Control Module. Not sure on a 2002, but on my 2000 it's on the passenger side fender.

Don't do the cable trick. Yes, you can damage the computer.

Have you pulled codes? Key on, off, on, do it three times. The codes should display in the odometer or most auto parts stores will test for you. Let the truck help diagnose the problem for you.
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Old 08-05-2011, 11:26 PM
hotrodbob38 hotrodbob38 is offline
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May I ask, What is the cable trick?
Bob
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Old 08-05-2011, 11:46 PM
AandPDan AandPDan is offline
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Quote:
Originally Posted by hotrodbob38 View Post
May I ask, What is the cable trick?
Bob
That's battery cable trick.

When cars had generators you could test the generator by running the car with the battery disconnected.

It's different with an alternator and with todays cars. You can spike the electronics very easily.

The battery is not just to start the car, it is also acts as a big capacitor to eliminate and absorb those spikes.

Last edited by AandPDan; 08-05-2011 at 11:47 PM. Reason: clarify
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Old 08-06-2011, 12:19 AM
Velocity09 Velocity09 is offline
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Bad News. Took it in to a trusted mechanic and he said it's the PCM. He wants to go thru the dealership ($500 plus for part plus more for flashing) total of near $900! ouch. So I asked about going with an aftermarket and he said he would look into it but with computer stuff he likes to stick with oem so it won't give any trouble. I searched online and found some as cheap as 159 on ebay and a place for 225 which required I give them the mileage and VIN so they can program it (is this flashing, what dealership would do?). what do you guys think? Should I order it online myself and how hard would it be to install it? would I need to take in to the dealership to have them flash it to my computer?
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Old 08-06-2011, 12:24 AM
Velocity09 Velocity09 is offline
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Just a dumb question, how do I clean something like that? I think I've seen electrical cleaning sprays but how do they work? just spray and let all that loosen up? I tried picking at it with a small flat head screwdriver and got most on the outside cleaned up, just don't know about the inside.
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Old 08-06-2011, 12:38 AM
AandPDan AandPDan is offline
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The sprays are about it. You can try a toothpick or something soft but don't want to spread the terminals so they lose contact.

I don't think you'd have any trouble with an aftermarket pcm. No, you wouldn't need to take it in, they'll program it (flash it) for you. A couple of bolts and connectors and you're running, just disconnect the battery first.

Did you ever check for codes?
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Old 08-06-2011, 12:58 AM
Velocity09 Velocity09 is offline
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No because it's at the shop, it never did give me any codes though. I didn't think about checking for some since I figured the check engine light would have illuminated which it never did. So I found one for 159 on ebay, with lifetime warranty or I can send mine in and they'll "fix" it for 124. The company seems legit. Does anyone have any experience with these refurbished pcm's? I feel like ordering it but want to make sure I don't have anymore issues.
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Old 08-17-2011, 09:11 PM
Velocity09 Velocity09 is offline
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Received PCM yesterday, plugged it in and everything was running fine. Today my check engine light came on. P0601, some type of internal computer failure, do you guys know if it'll go away? is this typical after a computer replacement?
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Old 08-17-2011, 11:41 PM
AandPDan AandPDan is offline
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I show P0601 as a checksum error.

It may have a fault in its programming or its damaged. Give the PCM rebuilder a call and ask.

I think you're looking at another replacement.
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Old 09-02-2011, 12:11 AM
Velocity09 Velocity09 is offline
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Got a replacement and the CEL went away yet I noticed my voltage meter was a little low, close to the 1/4 mark. I drove it for a 30 mins. or so and on the way home the check gauges light lit up and my voltage had completely gone to the left. Is it the alternator? could I have shorted it when I replaced the wires to the new pcm? I removed the negative cable before the swap.
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Old 09-02-2011, 12:59 AM
AandPDan AandPDan is offline
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You replaced the alternator before, right? It's possible that it has a problem.

There is one more piece of the puzzle but you need to pull codes. The battery charge is controlled not only by voltage but also by battery temperature. There is a sensor in the battery tray.

Hopefully the codes will narrow things down.
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Old 09-02-2011, 05:55 AM
Velocity09 Velocity09 is offline
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I returned the alternator I had initially bought since my mechanic told me it was the pcm that needed to be replaced. The codes I received where P0622 and P1682 I replaced it with my previous PCM the first one they sent me, at least the truck runs great but with a check engine light (P0601) I'm gonna send them the original pcm and this last one they sent me. I'm going to call them tomorrow and have them send me another pcm! It's getting frustrating.
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Old 09-02-2011, 02:13 PM
AandPDan AandPDan is offline
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If you've switched PCM's and it's charging then it is likely the PCM.

P1682 - charging system output low.
P0622 - generator field circuit not switching properly. An open or shorted condition detected in the generator field control circuit.
P0601 - internal controller failure. Internal control module fault condition detected (check sum).
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Old 09-02-2011, 02:38 PM
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The pcm has the voltage regulator built in if it goes bad you wont charge either
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