Wednesday, June 28, 2006

1993 2.5L Dodge Dynasty alternator over charging

Car wiring question:

I just subscribed to your program and the reason I need your service is my alternator problem. I have a 1993 2.5L Dodge Dynasty that is giving me fits! It had an alternator code for overcharging code and an engine code because the engine light is on. I can verify that it is overcharging because my battery is boiling. I changed the alternator because I thought that would fix the problem but to my surprise it is still the same! Now I am not sure if the rebuilt alternator I got is bad or I have a different problem in my hand. Please help.

Vehicle wiring advice:
Contrary to a lot of designs, your alternator’s voltage regulator does not reside in the alternator housing itself. Regulation comes from the your pcm (computer) which also control alternator field control. In your alternator, you will see these wires:

Black gray wire is from your fuse box Black wire is from your battery negative terminal Dark green orange wire is the field voltage wire from your computer (pcm) Dark green wire is your voltage regulation wire also from pcm.

Once there is a failure, the pcm will communicate with you by flashing the “check engine” light to warn you of the problem. In this case before condemning the alternator, you have to check the dark green wire from the pcm. To do this, go to your pcm terminal pin 20 and measure the resistance between the pin 20 terminal against the ground. Do this with your key turn off. If the resistance is less than 5 ohms, that wire is shorted to ground indicating a pcm failure.


The pcm is located at the left front corner of engine compartment.

Whenever you touch the alternator or the pcm, disconnect the battery negative terminal to prevent damages to the components.

Reset your pcm after the each repairs and go for a road test before getting the code again. If the problem is fixed, the “check engine” lights will disappear.

What ever you do when working under the dash panel, do not touch the yellow-taped wiring harness to avoid accidental deployment of the air bag which will activate even with the battery disconnected. Remember: you do this service at your own risk.


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