I have a LB7 Duramax 2004
The engine light is on now. The Truck is all stock. The Voltage gauge stay at about 12 volts for 20-30 seconds when i start it and then slowly comes up to 14.6 volt in 10 more seconds. I replaced the altenator and that did not fix it.
Any Ideas.....????????

It's not the alternator......

What you referenced is normal.

There was probably nothing wrong with your other alternator.

You need to have the codes pulled off. Go to you local parts house (or dealer, if you dare) and they should be able to scan it.

Let us know what they say.


Have you changed the fuel filter lately?

If you don't have something to scan it go to your nearest parts store and they may scan it for free. Get a code so you atleast have a direction to go

O'reilly auto parts has a nice scanner for 69.00$.. works great.. fixed my truck.works with a chevy vehicles also..

I have an extra fuel filter. I will put it in this afternoon.
The truck runs fine. I kept the old 105amp alternator. Maybe I can put it in as a second. I can weld up the brackets. What about wiring it? I guess I will get a code reader after I change the fuel filter.

I have an extra fuel filter. I will put it in this afternoon.
The truck runs fine. I kept the old 105amp alternator. Maybe I can put it in as a second. I can weld up the brackets. What about wiring it? I guess I will get a code reader after I change the fuel filter.

Then you would need to find the correct belt size for the 2 alt. Also fill out your sig. so we all know what you got.

Autozone will scan your truck for free, thats where I go.

I changed the fuel filter and the light is still on.
My friend said he will bring in his meter and hook it up and read the code for me on Wednesday

Fill in your signature as mentioned.
If the problem clears, usually the SES light will go OFF after a few heat-up cycles.
As said, the normal voltage delay at start-up is normal on cold start-ups. With outside temps at 0 deg F., this delay could be a minute or more.
Been using the engine coolant heater lately?

what you are seeing is the intake heater drawing your voltage down on startup which is normal

On December 23 about 11am, I checked my truck for the trip. I replaced 5 marker lights that were out. I guess I should check them more often. I checked the oil. It was low so I added some. While adding some I spilled some, so I hosed off the motor. I started the truck and went to the store. I noticed the light was on that after noon. I thought the maybe I put in to much oil. I checked the oil and it said over full by ¼”. I put it in the driveway nose first this making the front end slightly higher. I changed the oil filter and the level was right on the full now. I started the truck and the light was off. So I drove it 1800 miles in the next 6 days. The Light went on again and stayed on. I checked the code yesterday 01/07/09 and the code said P0380 “Glow plug circuit A malfunction.” What do you think???? ( the temperature in Santa Barbara is 48 at night and 60 during the day, i should not need the heater)

On December 23 about 11am, I checked my truck for the trip. I replaced 5 marker lights that were out. I guess I should check them more often. I checked the oil. It was low so I added some. While adding some I spilled some, so I hosed off the motor. I started the truck and went to the store. I noticed the light was on that after noon. I thought the maybe I put in to much oil. I checked the oil and it said over full by ¼”. I put it in the driveway nose first this making the front end slightly higher. I changed the oil filter and the level was right on the full now. I started the truck and the light was off. So I drove it 1800 miles in the next 6 days. The Light went on again and stayed on. I checked the code yesterday 01/07/09 and the code said P0380 “Glow plug circuit A malfunction.” What do you think????

You have a bad glow plug controller.

Potentially a glow plug controller. How well does the truck start? Are you seeing any fuel in your oil at all?

i do not know how to check for fuel in the oil. The truck starts fine, i went to the snow the other day and it started up after siting over night at 28 degrees just fine.

California truck? If it is it's a glow plug gone out. Not a big deal. See #3 in my sig. If your not covered then most any shop or you, should be able to test and change the bad one(s).
Ever drive north on highway 1 for about 45 mins? Howdy neighbor.:welcome:

I took my truck to the dealer in Santa Barbara. (Graham Chevrolet). The sale guy told me two glow plugs have a low enough voltage to trigger the code. They replaced all eight glow plugs FOR FREE. The Tech said “P0380- glow plug circuit, tested glow plugs and found multiple plugs open. Removed and replaced all glow plugs to prevent any possible failure-“ Thanks for all the help. rhapeman Signing off.