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Battery good, Alternator Good, gauge shows low voltage.

91K views 23 replies 13 participants last post by  Bigsot31 
#1 · (Edited)
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 ·
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.
 
#4 · (Edited)
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.
 
#5 ·
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?
 
#6 ·
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.
 
#7 ·
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?
 
#8 ·
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.
 
#11 ·
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.
 
#12 ·
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.
 
#13 ·
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.
 
#14 ·
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).
 
#16 ·
I had a similar experience. My battery had an internal short and that smoked the alternator. So I put a new battery in first and it would drive and then a mile or two and the check gauges light would come on and the amperage gauge would go flat. So I put in the new alternator and everything is running as it should.
 
#17 ·
make sure your spark plug wires are good if they're arcing out they'll cause all kinds of funny stuff. Mine fried my alternator and I knew it was them because I had wicked radio interference. just my two cents
 
#18 ·
I'm having the same problem with my 2001 durango. The voltage meter drops to the left after a few min of driving. The truck runs good but it seems to only be running on the battery. I have replaced the battery fully charged and replace the alternator and alternator wires. If it is the voltage meter and it's built into the PCM how do you fix it? Is there anything else that would cause the alternator not to communicate with the battery? Thanks all. I've seen a lot of people with the same problem but have yet to see anyone with a fix.
 
#19 ·
alternator not charging my battery

new battery, new alternator (2 actually), checked wiring,checked fuses, checked volts only 12v going through the whole system. I have power coming through the white cable going to the back of the alternator and not the green. I grounded the dark green as i have read to do and the alternator never turned on. Is my last resort to change the pcm? My car never threw codes when i took it to autozone. Also my voltage gauge drops to bottom if i start driving around. Any words of wisdom will help. Thanks in advance!
 
#20 ·
I would love any help too. I have a 2000 dodge Dakota. The issue started with the internal volt meter dropping below 14.xV to like 12v, showing the alternator was no longer changing. After a bit, the check gauges light comes on and the internal voltage meter drops to nothing (even thought the battery still has 12V when checking with a multimeter.

I've, of course, cleaned all the connectors and checked grounds. I suspected the alternator, so I checked the belt tightness and then even removed the alternator to use a multimeter and check it.... It seemed fine. Nonetheless, I took it to autozone, and they bench tested it, and it was putting out the right volts (so it passed the bench test as good). My first battery didn't pass a test (perhaps a cell was bad), but the guy thought it was still ok. In any case, I bought a brand new battery just to rule that out. So I have a new battery and a bench tested working alternator, but the alternator is still not charging.

At this point, I assume it's a wiring problem, or a PCM problem. I don't want to replace the PCM if I can't confirm it's the issue. Is there anything else I can do to confirm the PCM is the issue?
 
#23 ·
well, here are some hints for you guys that I found with a little research..some of the answers have already been mentioned...but I think its important to check your codes FIRST, then have components bench tested, load tested, ect....in that order.

it would seem that the PCM (Post 1996 vehicles only) relays information from your vehicles sensors and makes note of them as temporary problems or repeated problems and sends the codes to your vehicles on board storage system which you can retrieve on your dash board.

I found both OBDII scanner and manual tests for the PCM...

and I quote:


Dodge's powertrain control module (PCM) serves as the central computer for a vehicle's diagnostic system. The PCM analyzes sensor readings and engine functions. As soon as a component within the engine or fueling system malfunctions, the PCM issues a code and labels the problem either "trouble" or "pending." If the PCM were to cease working properly, your Dodge's diagnostic system would become untrustworthy. Testing this valuable device can be accomplished in a few minutes

Prepare some important materials before you check your Dodge's PCM. Consult your OBD-II (on-board diagnostic) scanner's handbook for a list of generic trouble codes. Also, find and print out Chrysler's supplemental OBD-II codes online and print them out. Take a highlighter to both and mark all the trouble codes that deal with the PCM itself. For example, P0601 denotes failure within the PCM itself. While testing the system, you should keep an eye out for it.

Place the coding resources in your Dodge's navigation seat. Then, get into the vehicle's driver's seat.

Locate your Dodge's computer outlet beneath the dashboard. The location of this data link connector depends on year and model of the Dodge. It may be beneath the steering wheel, next to the left kick panel or above the gas pedal.

Connect your OBD-II scanner to your Dodge's computer outlet. Switch the device on, and then turn the Dodge's electrical system on. You may own an OBD-II scanner that requires the engine to be running as well. Always keep in mind that no two scanner brands function exactly the same.

Look at your device's display screen. If there are no codes waiting for you, you own a scanner that is not preset for automatic code retrieval. Locate the procedure for entering a "Code scan" command. It usually entails pressing a button.

Scroll through the codes on the scanner's display screen. The PCM is part of the vehicle's powertrain. So you can safely exclude any OBD-II codes that start with "B," "C" or "U." Reference the source material you previously placed in the navigator's seat and look specifically for codes relating to the PCM's operations.

this also from Just Answer:

What you would need to do is check it's powers and grounds and then make sure there are no shorts on a couple circuits, and if all is ok then the powertrain control module (PCM) can be condemned and replaced.

With your symptoms the PCM is definitely down. That's why the fuel gauge and voltmeter don't work, and you are seeing the bus message because the PCM isn't communicating with other modules on the bus.

I see that you've checked fuses already but it's still best to verify the PCM power feeds. The PCM is the silver module under the hood with three 32-way electrical connectors. Find the black connector and unplug it, turn it over and you will see the terminals are numbered. Find pins 2 and 22, these should both have battery voltage with the key on.

At the same time, also check the two PCM grounds. These are pins 31 and 32 in the same connector. Pin 32 may not be numbered making it look like there are 31 pins in the connector, but 31 and 32 are the last two in the connector.

If all is ok disconnect the throttle position, MAP, cam or crank sensor and check for a short to ground on the orange wire. This is the 5v reference wire and the PCM will go down if it shorts to ground. If it does happen to be shorted then you've got an internally shorted sensor or wiring issue. These are possible but not that common.

If this is ok, plug the PCM back in and turn the key on. At whatever sensor you choose, check for the presence of voltage on the black/light blue wire. This is the sensor ground wire, again a short to voltage here will take the PCM down, and it can be caused by wiring or an internally shorted sensor.

If all is ok yet the PCM isn't awake then the problem is internal and it will need to be replaced.

Read more: http://www.justanswer.com/dodge/7cyki-dakota-test-engine-control-module-when-turn.html#ixzz40Z96cr7f

I hope this helps out...

JP
 
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