Neutral Gremlin

[Fumes]

I have a 2006 GMC with the LBZ and 6spd Allison, and here is what's happening; I'm driving along at 100 km (65 mph) and all of a sudden the trans goes into neutral, you let off the gas and step on it again it goes back into gear and then everything is ok. It does this off and on, about every 10 miles or so. Other than that the trans is working normal. This is at normal operating temperatures. I have had the codes P0700 and once P0502 appear occasionally but not always.

 

[Mike L.]

That is an Allison MD code. What are you reading the code with?

 

[Fumes]

So far I read it through the Banks IQ, I also have the Banks 6 Gun on the truck.

 

[Mike L.]

So far I read it through the Banks IQ, I also have the Banks 6 Gun on the truck.

Not good enough for diagnosis. Need real codes. Get a professional scanner installed.

 

[Fumes]

I have to find a place to do it or is there reasonable priced software that can be used?

 

[TheBac]

P0700 just tells you the TCM has set something. Tech 2 is the only way I know to read TCM codes.

 

[Robby05]

Snap on Modus & Solus will read trans codes

 

[Fumes]

I don't have enough money for that! Will have to find somewhere that has a Tech 2.

 

[Hot COCOAL]

I don't have enough money for that! Will have to find somewhere that has a Tech 2.

Any GM dealership will habe one
My local dealer would pull the code for free, but it might take 45min on a bad day to get someone to do it

I thought an AutoCal or V2 could/can/would read a trans code? Or do they only read the fault and not the actual code?

 

[mike diesel]

V2/autocal will read trans codes.

 

[Fumes]

Here is an update, first I don't drive the truck everyday but I had it out today to try a few things, it drops into neutral when it's in 4th gear, 5th gear or 6th gear. Also whether it's in 2 wheel drive or 4 (high) drive. But when you go to manual and shift it manually everything works normally.

I still haven't taken the truck to have the TCM codes read, maybe that will tell me something.

 

[DAVe3283]

Here is an update, first I don't drive the truck everyday but I had it out today to try a few things, it drops into neutral when it's in 4th gear, 5th gear or 6th gear. Also whether it's in 2 wheel drive or 4 (high) drive. But when you go to manual and shift it manually everything works normally.

I still haven't taken the truck to have the TCM codes read, maybe that will tell me something.

If the transmission set a P0700, then it is trying to tell you something. Get the codes read, and we can help you out! :hug:

 

[Stancedlb7]

Neutral under load usually needs a rebuild. I had the same codes with something along the lines of "fifth gear wrong ratio".

 

[Fumes]

Update 2

No codes, oil is good, took it to an authorized Allison dealer, they replaced the 3 sets of twisted pair wires for the speed sensors (from the senors to the TCM).

They pulled out the rear speed sensor as when they had the computer hooked up to it was reading that the truck was moving and it wasn't. There were some scratches, marks on it, so they looked a little further and there was only maybe 5 or 6 oz. of oil in the transfer case, (no sign of any leaks either). So they suggested that the transfer case needs replacing as something is moving around in it.

So this is where I'm at now.

 

[Awenta]

Bad transfer case can go into neutral. Worn fork. Check if the transfer case has any oil in it.

Crack it open and take a look inside. It's fairly easy to open up.

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[Fumes]

I was planning to just get one from the wreckers, one with a warranty. I get to keep the original one and will pull it apart at some point.

 

[onebaddmaxxx]

the plastic pads probably wore out on the forks...hence allowing the fork to get enough play in it to bounce between range. If you drain the fluid, it will probably look like silver slush. If so, your in for a rebuild. At minimum, i would install a case rub plate.

 

[Awenta]

^^Look for a pin hole on the top rear half of the case. Just realized you said there's only a few ounces of fluid in there. Even if you pick up a new or salvaged one install a pump rub kit or it will happen again.

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