Engine/Transmission (1998.5 - 2002) Interesting issue involving Cluster B fuse.

[PBJ2500CTD]

I am concerned with the jumpering (hot wire) of the alternator. If you took the output of the alternator and connected to the field wiring you have a situation where the alternator will be unregulated - over voltage/current situation that can fry a bunch of stuff - High voltage DTC's?
Also, the alternator field control (B+) circuits from the PCM are tied to the transmission relay, which may have caused the drivability issues and transmission codes.
I thought maybe the 140A fuse may have been faulty until the brain said you were getting voltage with the alternator jumped.

So, somewhere in or around the PCM and/or C2 pin 10, C3 pin 25 & associated wiring/plugs;Fuse M, S116, Joint connector 1 in the PDC.

My 1st choice is the PCM, as long as an overvoltage didn't cause all the magic smoke to leak from any of the other circuits. After the PCM I would look at all the wiring and plugs around the alternator and PCM as well as checking the PDC (check all fuses and physical connections in and around the PDC). Don't know if you have a rodent issues in your area but it wouldn't hurt to check for any mouce-munches present on the wires.

 

[BigPapa]

The alternator "hot wire" is a jumper from the positive post right side battery to the lower small stud on the back of the alternator. I monitored the volt meter very carefully. It never got over @ 13. 5V, never bounced or spiked. Basically, I'm doing the same thing the PCM does to make the alternator charge, sending a 12V signal to the alternator.



Scott

 

[firefighter_2000]

Side topic

I don't really have anything to add to what the problem might be, but on a side note: The key on-off-on-off-on cycle to read codes didnt start til the 2000 year model trucks. Pre-2000 trucks you have to use a code reader. Just wanted to throw that out there. Hope that helps.

Craig

 

[BigPapa]

Thanks Craig. Shoulda thought of that.



Scott

 

[BigPapa]

I have a friend with a '98 24V auto. What are the chances of locking up or messing up his PCM if we try it on my truck? If it locks his up, what do I have to do to get it unlocked?



Scott

 

[PBJ2500CTD]

Does everything work OK when you jumper the alternator? The alternator field B+ (pin 2) supplies the voltage to energize the trans relay. If there is insufficient voltage, as with low batteries, the relay may not be pulled in. Everything points to a faulty PCM or wire.

Wire continuity:

Term 1 of Alt field to PCM plug C2, pin 10 (generator field driver)
Term 2 of Alt field to PCM plug C3, pin 25 (generator field output)
Term 2 of Alt field wire also passes thru S116 to C130, pin 35 (PDC) to socket 86 of the Transmission Relay in the PDC

With the vehicle running and the tras relay removed there should be B+ volts at the tran relay's socket 86 in the PDC.

 

[BigPapa]

Got it fixed. Found this connector was not locked together good... ... ... ...



Thanks again for all the assistance.



Scott



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[BigPapa]

Well, now that I got all that straightened out there's still an aggravating issue with the transmission that I may just have to live with.



The transmission will not shift from 1st to 2nd after you first start the truck up until the speed gets up to @ 20 mph. When it does shift it is a very hard shift if you're in the throttle. You can run it up to almost 20 and let off and it will shift. After it does it that first time it shifts great until you shut the truck off again and then it does it again. As long as you don't shut it down it will shift fine.



Any ideas?



Scott