No power to TREC Fuse

[WestLinnYukon]

Hi everyone, I have a 2003 Yukon XL 5.3 4wd. From what I can tell I have a pretty unique issue.

When I bought it someone had jumpered a wire from the prime port (aux power for testing) to one leg of the TREC fuse so the 4wd would work. I figured this out when I tried to put it in 4wd and it blow the PCM1 fuse which diabled the prime power.

The real issue is that the reason someone did that was I have no power to either leg of the TREC fuse. I took the fuse panel apart, no obvious signs of an issue and no critters living in there. From what I can see in the diagram one leg should just have power from the battery, but I may just be reading it wrong.

Im I over thinking this? Is there something else preventing power from getting to the fuse?

Thank you very much!

 

[Donal]

Did you check the "4WD," fuse in the dash fuse box?

 

[WestLinnYukon]

Hi, thank you for the reply. Yes that fuse is fine. Also If I jump a wire from the battery to the 30amp TREC fuse my 4wd lights up. But there is no power to the trek fuse, and the schematic looks like it should have constant hot. I attached the schematic I have.

 

[Doubeleive]

I am not familiar with this issue at all but it would make sense that if the one side of the trec is supposed to be hot then I would trace from the hot source to the trec and try and fine the break? or perhaps it's grounded out therefore causing the other fuse to blow?

 

[WestLinnYukon]

Thank you. Yes that is my plan for the day. I was hoping there was an easier way, but I suspect your right. I will follow up when I track down the issue...

 

[rockola1971]

The Trec 30a fuse is fed from hot all the time but if the fuse is good then BOTH legs of the fuse should be hot since a fuse is electrically just a piece of wire. Without that 12v going to the Tcase shift control module, you will never get 12v to the encoder motor (AKA Electric shift motor on Tcase) since the TSCM is what provides the 12v directly to the Encoder Motor. If you can read voltage at the top of the fuse then you should measure 12v to both sides of the fuse. If you only measure it on one side then the fuse is blown OR the socket that the fuse plugs into is corroded. But since you dont read 12v at the fuse (when its not jumpered) then you likely have a broken wire to the fuse block for the 30A Trec fuse. I will have to dig out a schematic to find how it gets from the battery to the Trec fuse.

 

[WestLinnYukon]

Hi there, you are correct. I found the schematic and as a result opened up the fuse block. Looks like the hot leg was broken at the circuit board inside the block (you can see it wiggling in there). The leg feeding the TCM was fine. So rather than taking it all the way out, soldering it or replacing it (and risking messing other stuff up), I ran a wire from battery, with an inline 30a fuse, and made up a single leg to plug into the TCM leg of the block. Everything works, and as far as the car knows it is a standard configuration with appropriate fused protection.

Thank you eveyrone for you help. I have worked on lots of GM's and this one was pretty oddball...