Allison 6sp: Auto Range Select Switch?

[klanders]

Hello all,

Fist off, forgive me if I'm in the wrong place for this post, I'm new.

I have a 2006 4WD with the LBZ and Allison.
The other day the trans went into limp mode, so I took it to my local auto parts store and did a scan and came up with the following codes:

P0700 & P0878

The truck will do one of two things, either go into limp mode with check engine light and the afore mentioned codes, or the forward gears will work fine but I have no reverse. When shifted into reverse, I get the following message on the display, "Shift Range Inhibited".

My local dealer's service guy says he is 99.9% sure this is due to the Auto Range Select Switch that is internal to the transmission. I think on earlier years this was external and was called the Neutral Safety Backup Switch.

I purchased a new switch along with the internal and external filters and am prepared to go at it this evening. I thought it would be worthwhile to ask advice prior to going down this road. I have built engines before, but never cracked open a transmission.

Given the symptoms above, do you believe I am headed in the right direction?

If anyone can provide tourqe specs for the pan, plug and valve body, that would also be greatly appreciated.

Thanks,

Kirk

 

[Mike L.]

Your dealer is correct but it could also be the pressure switch manifold.
Tq on valve body bolts is 97 in lb
Tq on pan bolts is 20-25 ft lb

 

[klanders]

Thank you for the quick reply. Is the pressure switch manifold something I should look at while I'm in there or is it external?

 

[Mike L.]

It is internal bolted to the bottom of the valve body with a flat harness connector. Chances are it's ok.

 

[klanders]

Mike, I really appreciate your help. Last question, I hope, when I go to take out the valve body, are thing going to go flying, or does it come out as one complete unit?

 

[duratothemax]

Mike, I really appreciate your help. Last question, I hope, when I go to take out the valve body, are thing going to go flying, or does it come out as one complete unit?

not to answer for mike....but it comes out as a complete unit. No check balls will go flying or anything.

The only thing you have to watch for is the manual shift valve alignment pin...BUT on the 6-speeds allison was friendly enough to put a little plastic plug in there to keep it from falling out during VB reinstall.

 

[klanders]

I really appreciate you both. I guess I'll be up to my elbows in Allison tonight. That just sounded wrong.

 

[Cougar281]

An extra pair of hands would be usefull to R & R of the VB, just to be sure it doesn't get dropped, and to help with alignment of the pin on install. I've done it alone, but it's easier with a second person.

 

[klanders]

So far, it's going pretty good. I have the VB out. I now need to remove the shift rod from the case. I see a pin that appears to hold the end of the rod into the case, but figured I would ask for advice before attacking it with vice grips. What is the "proper" way to remove the shift shaft? Also will the rod with spring that goes from the auto range select switch into the rear of the tranny just come out once the switch is loose?

Again, thanks for the help here!!

 

[Mike L.]

Pull the vb dowl pin out as it locks the shaft in place. The rest is easy.

 

[klanders]

Well, now for a question I was hoping not to have to ask. The pin that goes through the zig zag slot in the switch fell out when I dropped the valve body. It would not go back in with removing the little plastic keeper at the end of the hole the pin goes through on the VB. Upon trying to remove the keeper, the head broke off, leaving the rest of the keeper in the hole where it goes. Other than making it a bit more of a challange to get things back together, should this cause any grief to operation of the tranny? It seems once the pin is in the switch, it will be captured so as not to be able to go anywhere.

 

[klanders]

I got the trans back together and it is doing the same thing. Anyone know of a good dealer in the Dallas/Denton area?

 

[Cougar281]

I'm not Mike, but with the codes above, it sounds to me like the reverse pressure switch may have blown out it's O-Ring (or the switch is bad). I don't recall the code, but when I put the PSM in and the O-Ring for the reverse switch wasn't where it belonged, I had similar symptoms. Forward gears where fine until I shifted into reverse; when I shifted into reverse, it would throw a CEL, Range Inhibited and put the TCM into limp mode.

 

[klanders]

Any idea the cost and part number for this? I appreciate the advice, I'm just getting frustrated with this project.

 

[JoshH]

I'm not Mike, but with the codes above, it sounds to me like the reverse pressure switch may have blown out it's O-Ring (or the switch is bad). I don't recall the code, but when I put the PSM in and the O-Ring for the reverse switch wasn't where it belonged, I had similar symptoms. Forward gears where fine until I shifted into reverse; when I shifted into reverse, it would throw a CEL, Range Inhibited and put the TCM into limp mode.

I had the same thing happen to me before as well. As I recall, the o-ring isn't available as a seperate service item, but I think the switch manifold was only 30 or 40 bucks from Allison.

 

[klanders]

So do you folks think the next reasonable step is to replace the pressure manifold switch, or have it looked at by a shop? I hate to keep throwing time and money into it if there is not a resonable expectation that I can fix it this way.

 

[Cougar281]

Well, it would likely be cheaper for you to replace the PSM than to have a shop look at it. You might not have to replace it though; When I had my problem, I was able to put the O-Ring back where it belonged and all was good (Obviously, that wouldn't help if the switch is bad).

 

[klanders]

The truck is behaving a little different now. I do not get the Shift Range Inhibited message any longer. The truck will run fine in forward, when I shift into reverse it will pause, then go into reverse, then after about 3 seconds it will go into limp mode. If I turn the truck off for a few seconds it will again work fine in forward. I ordered the manifold pressure switch, I guess I will see if that does the trick.

 

[Mike L.]

Gues it's time to diagnose this problem instead of throwing monry at it.

 

[klanders]

I ordered the Manifold Pressure Switch for the 2000 and up. Of course it was the wrong one. Mine has 4 o-rings, the one I got had 6 I think. Anyone know the correct GM part number for my 2006?