Another Transfer Case Blown Fuse Problem

[zsanity]

First thing - I have a 1999 Chevy Suburban 2500 4x4, 7.4L with the 4 button switch 4wd. Old body style.

Problem - #2 20 amp transfer case fuse keeps blowing.

I am going to try and explain everything i have tried to troubleshoot this, and am still left completely in the dark. All troubleshooting has been done by searching these forums already. Fuse only blows when I am driving over probably around 10mph.. will not blow idling, starting, or switching between 4wd and 2wd. Will not blow going into park, or reverse or neutral.

I started with unplugging the encoder motor at the T-case. Both the C1 and C2 connector. Fuse still blew. I plugged that back in, and unplugged the C2 connector at the transfer case control module, Fuse DID NOT blow. Bought a new TCCM, plugged it in and fuse blew again?? Put the old TCCM in, and unplugged the front differential actuator, Fuse DID NOT blow. Took the actuator out, plugged it back in and the actuator goes in and out as it should when you engage and disengage 4wd.
I also unplugged the button switches on dash and fuse still blew. I also tried removing the 4wd fuse #24 and the #2 fuse still blew.

I also have checked most wires to ground, and cannot find a short. Did this with a test light hooked to battery positive. Somehow, either unhooking the C2 connector on the TCCM or the front diff actuator is taking something out of the equation to keep the fuse from blowing. Even though the actuator works, could there still be an internal short? And why would the fuse not blow until I actually started driving? Hoping someone can shed some light on this.

Some other stuff - Could low or dirty fluid in the front diff or transfer case cause any problems? Transfer case is only a year and half old, and the fluid is the special kind from the dealer. T-case seems to pass the stick my finger in and feels full test. I am leaning away from the encoder though since unhooking it did not help.

[j cAT]

what can happen is the wiring and the fuse box area can get damaged. wiring running down from the fuse box requires a loom plastic to protect from chaffing esp at the casting metal.

if the truck has had motor//tranny work this is quite common.. sloppy repair work on the wiring placing.
good luck

[777stickman]

The wire you need to look closely at is the Orange wire. This is the feed from the T-Case fuse which is "hot at all times". This wire goes to the C2 connector on both the TCCM & Encoder.

I would suggest that you spend the money to get the Auto T-Case system scanned for DTC's which requires a high end scan tool to access the info.

[zsanity]

Thanks for the replies!!

I tried a new actuator and that did not work either. I unhooked the C2 connector on both the TCCM & Encoder, and nothing is shorted to ground, other than the black ground wire on the TCCM C2 connector of course. Also tested the other connector on the encoder motor just to make sure and nothing there is shorted to ground either. I will go have the system scanned too see if there is anything apparent. So far I am testing all downstream from the fuse.. should I be looking towards the otherside of it at this point?

I am still very much confused why it will only blow after I am driving.. tested it again today, left the truck running for probably 30 minutes with no problems.. but after about a quarter mile down the road, boom.. blown fuse every time. Years of fixing wiring on airplanes in the Air Force has taught me that if something is shorted together, it usually will blow the fuse/circuit breaker instantly. Only thing I can figure is there may be something going on with the computer in the system, with all the automatic speed sensors and other wizardry that these systems have in them.

[zsanity]

Ok in from playing with it and one thing I noticed is that with everything hooked up, I am reading a ground on the opposite terminal of the #2 fuse. I hook up my test light to the power in side, and touching the other side I get a light. With the C2 on the TCCM unhooked, I do not get a ground. So I am sure that I am reading the ground from the connector through the TCCM. What I don't know is if that is normal or not.

[Blue Bowtie]

Originally Posted by j cAT

what can happen is the wiring and the fuse box area can get damaged. wiring running down from the fuse box requires a loom plastic to protect from chaffing esp at the casting metal.

if the truck has had motor//tranny work this is quite common.. sloppy repair work on the wiring placing.
good luck

Also, sloppy assembly at the factory can accomplish the same thing. This one was chafing against itself inside the convoluted tubing and inside the plastic tape wrap as assembled from the factory, 10" from the PCM:



Fortunately the two failed circuits in this case only involved the ABS and cooling fan operation, so it was really nothing important. As long as the GPS and radio work, the vehicle is just fine, right?

[Blue Bowtie]

In case you don't already have the diagram:

[777stickman]

Check your Private Messages.

[j cAT]

Originally Posted by zsanity

Thanks for the replies!!

I tried a new actuator and that did not work either. I unhooked the C2 connector on both the TCCM & Encoder, and nothing is shorted to ground, other than the black ground wire on the TCCM C2 connector of course. Also tested the other connector on the encoder motor just to make sure and nothing there is shorted to ground either. I will go have the system scanned too see if there is anything apparent. So far I am testing all downstream from the fuse.. should I be looking towards the otherside of it at this point?

I am still very much confused why it will only blow after I am driving.. tested it again today, left the truck running for probably 30 minutes with no problems.. but after about a quarter mile down the road, boom.. blown fuse every time. Years of fixing wiring on airplanes in the Air Force has taught me that if something is shorted together, it usually will blow the fuse/circuit breaker instantly. Only thing I can figure is there may be something going on with the computer in the system, with all the automatic speed sensors and other wizardry that these systems have in them.

well you know its a wire chaffing on so metal ground. testing is not gonna fix it . the harness running down to the encoder is a common problem .. the wires on the NBS are even more of a problem since the copper is very small GA.. these wires if not handled carefully break.

I had on my NBS a rodent nest under my under hood fuse box they did chew some of the wire insulation . I used liquid tape to fix.. just so happened to be the wire to the encoder.