Battery voltage while truck is running fluxuates. 10v-14v. Not good. alternator basicly turns on for 2 seconds and then off for 2 seconds. This repeats forever. I thought it might be the alternators regulator. Bad news, the regulator is not on the alternator but it is part of the PCU (powertrain contol unit).

I can not find the pcu on the truck. I looked everywhere. Dealer says its located under the engine block. Other shops say it is on the driverside fire wall. Well there is a computer there but a part number on the side of the unit confirms that it is the ABS computer and not the PCU. Or can it simply be a bad alternator? Anyone have experience with a problem like this?

 

Might be a bad alternator. PCM should be on the passenger side firewall, under the hood.

 

Does anyone know if it is the PCM or the alternator? Thanks for the suggestion hey you. However I would like some more information.

 

Take the alt up and get it tested, if it is ok.......

 

first confirm its not something funky going on with your grid heater it will cycle on and off until the engine has reached a certain temp drawing alot of voltage..to test first have engine warmed up then unplug the grid heater see if the voltage levels out..i assume its controlled by the temperature sensor so a bad one of those could mess it up

 

I took the alternator out as hey you suggested. Took it to all the well known auto supply stores. The first store tested it and the alternator failed, well at least that is what the computer said. Of course the sales person was trying to sell me a new alternator. I told the guy if the new one passes I would buy it. He hooked it up, it failed too. The sales person stated their connectors were bad.

I took my alternator to 2 more stores. Same outcome. Failed the test. New alternators failed the test too.

At one of the stores I was looking on their computers myself. I found this.

TBA0037 Technical Service Bulletin

CAUTION - NOTE TO STORE - This alternator is desigigned to be regulated the the vechicle's onboard computer. This alternator must be tested using field (1), field (2) system.

 

Basicly the test is run like this. On your trucks alternator disconnect the connection that has two skinny lug bolts side by side. There is a left bolt which is field 1. The right bolt is field 2.

The wire that was connected to field 1(left lug bolt) jump to the same wire that was removed.

Field 2 lug bolt jump to ground.
Now the alternator is hooked up in a way that bypasses the onboard computer.
You take a digital multimeter and hook it up to the battery. Start the truck. When you increase rpm the voltage on the meter should go up. If this does not happen, your alternator is bad. Do not go over 18v during the test.

 

I have not run this test yet. I need to install the alternator.