M923A2 Transfer case no engagement.

[Plane Fast]

Well I decided to tackle my transfer case lack of engagement. I started by doing the TM test for the transfer case control switch. Well I had no power at lead 585 or 586. To make sure the button was working, I just disconnected the switch and did a continuity test (with the button held in). It was good. So I moved on to the next test, checking for voltage at the fire wall CB. It has you test lead 37. I did have voltage there. I then now had to trace the lead from the handle to the fire wall to see why I had no power.

The leads going to the diode did not have power. I traced it all the way to the fire wall harness. No power. Lead 585 went into the wrapped harness. So I could go no further. I did notice that lead 587 was next to it, and it was capped off. I tested it and it did have 24volts. So looking at one of the wire diagrams, it showed 587 powering the transmission control switch. Which turns into 585. Looks like 587 gets it's power from 37. So is it possible that the leads should be switched? The 585 lead goes past 587, all the way into the firewall. I would seem unnecessary to have 585 go that far just to use 587.

Well any how. I tried it with 587 hooked up, and it worked. Transfer case worked as it should. The interlock solenoid valve was a little stiff. But it got better with working the system. So now I'm not sure what to do. Leave it as is, or go back to how it was hooked up before. (And do some more digging)

The last photo shows the location of the 587 and 585 connections.

 

[Plane Fast]

Oh and this is the diagram.

 

[VPed]

I have found that some trucks need the transmission shifter cable adjusted to ensure power gets through the switch on the shifter. It sounds like the problem you are experiencing. The indicator on the shifter should line up exactly with the "N" when in neutral or power will not be fed to the transfer case button.

There is no adjustment within the shift tower. It is adjusted at the transmission end.

 

[Plane Fast]

Thanks I will check that out.

 

[73m819]

He is talking about the transfer shifting lock

 

[Plane Fast]

Would that be the transmission control switch in my last picture diagram?

The one that feeds the 585 power lead.

 

[VPed]

Would that be the transmission control switch in my last picture diagram?

The one that feeds the 585 power lead.

That very one indeed.

 

[Plane Fast]

I was thinking, if it was out of rig at the shifter. Would it not work at all?

 

[Plane Fast]

By using the 587, I may be bypassing the switch I guess. I'm going to have to test.

 

[Plane Fast]

That very one indeed.

You were on the money! I hooked up the wire back to stock. Slowly moved the shifter in the neutral detent. At the same time I would push the transfer case button. Sure enough I found a sweet spot, and it worked.
Thanks

 

[VPed]

Now you just have to crawl under the truck and adjust the cable so it always lands in the sweet spot when in neutral. Pull a cotter pin, pull a clevis pin, adjust length to suit, reassemble in reverse order.

 

[Plane Fast]

Sounds good. Will do.
Thanks

 

[Ghost1986]

If I jumped out my pcb. Completely bypassed it( it was bad) would this cause my transfer case not to engage? It won't do ANYTHING. Any ideas?

 

[simp5782]

If I jumped out my pcb. Completely bypassed it( it was bad) would this cause my transfer case not to engage? It won't do ANYTHING. Any ideas?

wont do anything in what description? Like truck wont move or truck wont come out of high or what?

There is a wire to the top solenoid on the transfer case that goes to the capacitor that is attached to the floor of the cab above the transmission. It also runs to the Neutral safety switch and the parking brake valve. It does run to the PCM so it gets some type of powerfeed to all of those wires... The wire number at the transfer case is a 568.

If you need a PCM contact Fuzzytoaster. I think he has a few. It always good to have a spare laying around.

 

[Ghost1986]

Won't do anything as in it's in high, but won't shift into low ( pushing the button on the lever doesn't release air in the stack) looked it all over but it might be the pcm or lack thereof.

 

[simp5782]

Won't do anything as in it's in high, but won't shift into low ( pushing the button on the lever doesn't release air in the stack) looked it all over but it might be the pcm or lack thereof.

Run the truck to full air capacity. Turn it off. Switch on both switches. Do not start it. Listen for a noise when u push the switch on the lever. If no noise then it is not allowing the interlock sleeve to disengage. Its the valve on the top of the transfer case. Four 7/16 bolts. See if the flap seal on the round cylinder is broken.

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[simp5782]

You could also have some air lines routed wrong. It is a common problem

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