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sprinkles08, Chrysler/Dodge/Jeep master tech
Category: Dodge
Satisfied Customers: 22692
Experience:  ASE Master and Advanced Certified, Chrysler/Dodge/Jeep Master Certified, Trans and Hybrid Specialist
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2006 Dodge Ram 3500 5.9L Cummins 6-speed 4x4. Batteries and

Customer Question

2006 Dodge Ram 3500 5.9L Cummins 6-speed 4x4.
Batteries and alternators replaced twice.
All connections clean and corrosion free
Alternator tests good out of vehicle
Alternator in vehicle produces 19+ volts on batteries
ECM output PIN 7 K20 18br/gy Gen Field Control reads 12.8 volts at Alternator
What is the expected output of the ECM to the alternator?
How does the ECM make a decision to tell alternator to adjust voltage?
Maximum voltage for the 6 cell auto battery should be less than 14.9 and closer to 14.4V
Submitted: 1 year ago.
Category: Dodge
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

The ECM reads battery voltage to decide what to charge at. The alternator under normal operation is duty cycled on and off constantly to keep charging voltage in the target range. Voltage will usually be in the 13.5 to 14.5v range.

It's possible that you could have an alternator wiring, ECM or ECM wiring issue but the most common thing to cause localized overcharging on these is the positive cable between the batteries.

Start the engien and put the black meter lead in teh center of the right battery post, red lead to the positive post (not the terminals). Record the voltage.

Immediately go to the left battery and do the same. What do you see for each side?

Customer: replied 1 year ago.
Sorry for the delay. I was looking for the expected output of the ECM. Basically does the ECM send a simple on off signal for the alternator or does it send a voltage level that the alternator response to on current output?
Expert:  sprinkles08 replied 1 year ago.

The alternator is duty cycled by the ECM.

Customer: replied 1 year ago.
Makes sense, but do you know the signal(s) sent by the ECM?
Expert:  sprinkles08 replied 1 year ago.

How is the alternator controlled? Ground is duty cycled on the control wire, battery voltage on the other.

Customer: replied 1 year ago.
That is what I needed, thanks. Alternator and ECM are working fine.
Expert:  sprinkles08 replied 1 year ago.

You're welcome!

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