Engine/Transmission (1998.5 - 2002) Altenator?

[DSeamans]

Ran to town today, stopped at a store, started it back up and a couple minutes later the check gauge light comes on. Look and voltage was almost down to 8 volts on the gauge. Pulled over and shut it down and looked around. no bad connections or fuses. Just for giggles, I pulled the heat grid relay. With the key on but truck off, gauge shows 13 volts. Fired it back up and after about 2 minutes, it slowly went up to 14+ volts. Got it home and load tested the batts and they were fine. Cleaned and regreased (dielectric) terminals and wires and the same thing happens. The voltage goes lower and takes longer to come up than the normal heat grid cycles. Does this sound like a diode or regulator dying or is there something else that could cause that kind of draw? I was wondering about the starter, but it doesn't appear to be hanging. Thanx for any ideas.



Dave

 

[blacksheepdiesel]

Could be alternator going bad, or the two wire connector that plugs into the back of the alternator. Try pulling that connector and look it over good. Mine appeared good but gave the same symptoms you have. Since replacing that plug the alt has worked perfect.

Godspeed,
Trent

 

[B.G. Smith]

Sounds like the intake air heater grid relay is stuck closed to me. bg

 

[SSolderitch]

I was told that the AIT sensor is used for heaters before start up. BUT after start up it switches to the water temp sensor. But that is only if you don't go over 19 mph. Simple to check, but the problem may be in the pcm

Some have hooked up an older style external voltage regulator, taking it out of the PCM, that circuit can go bad.



But it also uses the temp sensor under the battery which could have gone bad. Simple check with a ODB III.

 

[RSimmons]

It is very possible that you are due for a brush replacement in the alternator. Any local starter/alternator shop should be able to replace them cheap.



There is not much in these trucks starters or alternators that fail other than brushes and bearings or solenoid contacts for the starter. The regulator is part of the PCM.



The intake air temp sensor is responsible for the grid heater duty cycle. If your IAT is dirty or faulty, it could cause a heaver grid cycle than normal. No matter what the cycle, it will stop after 2 minutes or you hit 19 MPH.

 

[DSeamans]

Altenator

It's not the heat grid as I pulled both the fuse and relay. There were no codes. Does it throw a code if the regulator in the ecm acts up? I have a new alt to throw in. Its too cruddy to do outside and I have the box off and in the shop prepping for paint.

 

[DSeamans]

What now?

Put the new alt in. Start the truck and it takes 20 - 30 seconds to come up to voltage. I can see the heat grid cycle on and off once its up. The new one must put out more amps as the volts drop less than one volt as the grids cycle. Why would it take so long to come up? Voltage regulator in ecm acting up or getting ready to die? It started instantly, normal one start then slow the next. I've never seen anything like it.



Back to body work,



Dave

 

[blacksheepdiesel]

If the battery has been abused somewhat because the alternator wasn't working it will take a while for the volts to come up until the battery is back up to full charge.

Godspeed,
Trent

 

[AKAMAC]

The PCM halts the charge system when the grid heaters are called for. I would suspect the IAT as the problem.

Try unpluging it and look at the charging cycle.