Electrical problems help!!!!

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Tim123

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Kings mtn nc
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1999
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V8 5.9
Hi plz bare with me I'm new to this. My alternator isn't charging my battery. Took it and had alternator and battery checked both checked out good. I have checked all fuses connections and can't find anything wrong there. My transmission has went into what I was told limp mode because there isn't enough voltage to change gears. I was told it could be pcm is there a way to check. I'm losing my mind with this. Any help is appreciated. Sorry I forgot to say it's a 99 Dodge ram 1500 5.9
 

dudeman2009

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2001 1500 Sport with enough electrical modifications to make my brain hurt
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Magnum 360
Whoever told you that the transmission is going into 'limp' mode because its not getting enough power is full of it.

Where did you take the alternator and battery to get them tested? Did they test them in or out of vehicle?

First thing i'd do is check the wiring coming from the alternator and make sure that the cable is in good condition and the leads are free from corrosion. Then make sure the 140A alternator fuse hasn't blown. If the charging voltage is low or non existent, check the two wire connector on the back of your alternator. Your year should have a little plug type connector with two wires, right next to the main charging cable. If that all checks out, inspect the ground lead from your battery all the way to the frame and engine connection points and make sure it is free of damage and corrosion.

The PCM controls charging voltage, if it has gone bad the battery will fail to charge, however, its rare that the charging system in the PCM goes bad.
 
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Tim123

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I took them out of the vehicle to have them tested at Auto zone. I have checked the fuse it checked good. I'm going to check the ground lead and go from there. Will low voltage keep it from going into over drive? Thanks for your help gives me an idea where to start.
 
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Tim123

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Problem fixed. Replaced pcm runs perfect and charges fine!!!!
 

dudeman2009

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Low voltage will cause the engine to shut down due to poor ignition before the transmission starts having problems.

However, charging system regulation failure as well as other system failures can be signs that the PCM has failed. If your charging and transmission problems both went away when you replaced the PCM, i'd be comfortable saying the old PCM was on its way out.

However, you will want to make sure that the grounds between the engine, battery and PCM are clean and tight, just in case poor grounding caused the damage to the old PCM.
 
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