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Chris
Chris, Shop Foreman
Category: Dodge
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Experience:  ASE and Chrysler Certified Master Tech
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1994 Dodge Ram 2500, 4x4 Cummins Turbo Diesel. Truck is overcharging,

Customer Question

1994 Dodge Ram 2500, 4x4 Cummins Turbo Diesel. Truck is overcharging, replaced alternator, cannot find any shorts in the wiring. Checked grounds, reconnected grounds. Codes are showing, 12 Battery Disconnect, 42 Short or open in Auto Shutdown Relay (replaced relay) 46 Battery Charging system voltage too high, 41 Open or short in alternator field control circuit.
Submitted: 5 years ago.
Category: Dodge
Expert:  Chris replied 5 years ago.

Hello and welcome to just answer Dodge. The code that is causing the overcharging is code 41. Now if you have disconnected the alternator field wires, and the PCM (engine computer) connector and checked for shorts to ground in the alternator field circuit then the PCM is shorted internally and will need to be replaced. There are only 3 things that can cause this 1 a shorted field inside the alternator (but you changed that) the wiring, and the PCM.

Hope this information helps, and let me know if you need more assistance with this.

 

Chris

Customer: replied 5 years ago.
Hello Chris thank you very much for your answer. My being less than professional at automotive tasks let me make sure I am following you. When you say alternator field circuit that is all the wiring from alternator to battery and to ground basically? Yes already changed the alternator so that rules that out. The PCM............is that the module that is located behind the kick panel inside the passenger's side? I did notice that I have a wiring harness of some kind hanging down from the dash to the box behind that kick panel. I placed it back up in the dash but it could have gotten pulled. I don't see any exterior wiring damage to the harness. Thanks for your help!
Expert:  Chris replied 5 years ago.
The field wiring is between the alternator and PCM for the field control, and the field voltage supply is between the alternator and the fuse box under the hood. The field wires are the 2 small ones on the back of the alternator. The PCM is mounted under the hood, is a black plastic module with one large connector bolted to it. It should be either on the fire wall, or left fender area.
Chris, Shop Foreman
Category: Dodge
Satisfied Customers: 10002
Experience: ASE and Chrysler Certified Master Tech
Chris and 3 other Dodge Specialists are ready to help you
Customer: replied 5 years ago.
Thank you very much Chris I will check that when I get home. I traced the wiring from the alternator and remember the two smaller wires. They at one point, go into a larger cluster of wiring surrounded by a sheath. I will just need to open that up and trace them further. I didn't remember seeing the PCM but I know what you're talking about and I'm pretty sure I can find it.
Expert:  Chris replied 5 years ago.

Sounds good. If you or someone you know has and can use an ohmmeter, then check the field circuit that way before opening up the harness. Simply disconnect the field wires at the alternator, disconnect the PCM and remove the ASD relay. Then check for continuity at the field wire going to the pcm (not sure what color that one is) and to ground. There should be NO continuity. If there is not, then the wiring is good and you should suspect the PCM as the problem.

Thanks for the accept, and let me know how it goes,

 

Chris

Customer: replied 5 years ago.
Chris, fortunately I'm a network administrator and have a little bit of working knowledge of wiring, continuity etc. Took your suggestions and found that the PCM was not the likely culprit. What I did end up finding is two small wires going to a sensor in the top of the head (I assume) beside the valve covers. One of these wires were broken and touching another wire, incidentally worn and bare as well. I unplugged the sensor which I suspect to be the heating element sensor but definitely not sure, and it was not charging near as hard. ( top of 14 vs. slammed on 18 on the gauge) It was getting dark on me and I had to return some business calls so I'm going to open up that part of the wiring harness tomorrow to repair the wiring. I didn't see that before but happened across it after removing the airbox and wiring to the PCM. Thank you so much for your help, I hope once I insulate and shrink wrap the wiring to that sensor I'll be back in business.
Expert:  Chris replied 5 years ago.

That is probably the problem! Glad you found this and let me know if that fixes it.

 

Chris

Customer: replied 5 years ago.
Very well I'll drop you a line tomorrow after I work on it. Thanks again!
Customer: replied 5 years ago.
Chris got that taken care of and it is not immediately charging to 18 volts. However it gets over to 18 in about 30 seconds or so. Any thoughts?
Expert:  Chris replied 5 years ago.

Ok, then let's try this next. Disconnect the PCM connector and start the engine. If it is still overcharging, with the PCM disconnected then the problem is the PCM. Let me know how that goes,

 

Chris

Customer: replied 5 years ago.
Alright that sounds like a plan. Make sure I have the right thing here. It is located behind the airbox on the firewall. I'll disconnect that harness and let you know what it does. Thanks!
Expert:  Chris replied 5 years ago.

Ok, let me know. Yes the PCM is on the firewall behind the air box.

 

Chris

Customer: replied 5 years ago.
Chris, I disconnected the PCM it is NOT overcharging with it disconnected. It is charging right where it used to. I read your prior response to mean that the PCM IS NOT the issue here. Am I correct in that statement? If so I am I'm pretty much stumped.
Expert:  Chris replied 5 years ago.

Well it should not be charging at all with the PCM disconnected. This sounds like it is the PCM. If it was still overcharging with the PCM disconnected then the problem would be a short to ground in the field wire to the PCM. Normal charging should be 13.8 to 14.2 volts. Are you reading the voltage with a voltmeter or are you going by what the meter on the dash says? I recommend reading the voltage at the batterywith a good hand held digital voltmeter.

 

Chris

Chris, Shop Foreman
Category: Dodge
Satisfied Customers: 10002
Experience: ASE and Chrysler Certified Master Tech
Chris and 3 other Dodge Specialists are ready to help you
Customer: replied 5 years ago.
14.1 at the battery with a voltmeter. How good it is I don't know I usually work on electronics and guitars. LOL!!!
Expert:  Chris replied 5 years ago.

14.1 is perfect. Now is that with the PCM connected or disconnected?

By the way, thank you for the accept.

 

Chris

Customer: replied 5 years ago.
That is with the PCM disconnected.

I'm new to this so I'm not real familiar with that accept feature. I realize now what it does. I thought that the first accept was all I had to do. I'm learning. I have given you positive feedback that's for sure.
Expert:  Chris replied 5 years ago.

Thank you for the accept! If it still seems to overcharge with the PCM connected, then suspect a bad PCM.

 

Chris

Chris, Shop Foreman
Category: Dodge
Satisfied Customers: 10002
Experience: ASE and Chrysler Certified Master Tech
Chris and 3 other Dodge Specialists are ready to help you
Customer: replied 5 years ago.
Good deal my friend, I'm going to get me a new PCM and go from there. Thank you for your help!
Expert:  Chris replied 5 years ago.

You are very welcome!

 

Chris

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