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01 2500HD Duramax transmission issue

E

eric67camino

1/2 ton status
 Premium
Joined
Feb 20, 2011
Posts
476
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1,390
Location
Kansas
Truck:
01 2500HD CCSB 4X4
LB7 Duramax
Allison automatic transmission
416k miles

Started the truck yesterday. Didn't let it warm up long. Backed out the drive. Goose the throttle to see how the roads were. (We've had rain, sleet, etc lately and I wasn't sure if it would be slick. It wasn't.)

Truck starts forward, then is in neutral. Shows in drive still, but acts like neutral. Put it in neutral, then back in drive. Same thing, no go. Tried reverse, same thing.

Shut the truck off. Sit there in the middle of the road contemplating my options. Start the truck up, try shifting the transfer case to 4 HI. Put it in gear and forward works. Ok, maybe the transfer case had went into neutral for some reason. Shift back to 2 HI. Drive 15 miles to work. Had a service engine soon light for a bit, but went away. Checked transmission fluid and found it low. Added a quart. Seemed to be fine. Drove home that night. No problems. Drove to work this morning. No problems.

Left work tonight, made it a quarter mile and we're in neutral again despite being in gear. Same story. No forward, no reverse, light came on. Fluid level is fine. Shut it off, restarted, tried shifting transfer case again, away we go.

Stopped at the Oriellys, pulled the codes.
P1713
P0700

Anybody seen this before? Or have suggestions on how to diagnose it, short of taking it to someone? I can fix about anything, but automatic transmissions are not my strong suit.
 
Searched the internet, possible cause that I've found is the NSBU (Neutral Safety Backup Switch), but not sure how to diagnose it without just replacing.
 
‘01’s had the transmission range switch mounted to the outside of the trans. Early Allison transmissions did have an issue with moisture getting into the range switch (aka nsbu switch). When the moisture freezes the switch don’t work. If the Allison tcm looses that input signal from the switch it don’t know what the gear selection was and either defaults to neutral or third.

Gm did have a bulletin on it. I’d be pretty confident replacing the switch. Just make sure the connector is ok and no damage.
 
eric67camino said:
Searched the internet, possible cause that I've found is the NSBU (Neutral Safety Backup Switch), but not sure how to diagnose it without just replacing.
Click to expand...
Following to see, as I was thinking that the switch could be suspect with that many miles.
@ZooMad75 is probably spot on, I would swap a new one on if there isn't something obvious at the connector after reading his post.
Allison transmissions will protect themselves if there is a problem sensed.
 
6872xtc said:
Following to see, as I was thinking that the switch could be suspect with that many miles.
@ZooMad75 is probably spot on, I would swap a new one on if there isn't something obvious at the connector after reading his post.
Allison transmissions will protect themselves if there is a problem sensed.
Click to expand...
Later Allison transmissions had the range switch moved to inside the transmission. I want to say around ‘05 but I could be a year off. I know the later GMT800 trucks didn’t have the external switch.

One issue I remember happening is the indicator on the cluster they basically put an underline under the gear selected will disappear when the switch is acting up.


A key component to the problem is if you let the switch warm up to not be frozen and it starts working normally it’s most likely the switch.
 
Thanks for the input. I will try her again today and see if it repeats. Supposed to be warmer this weekend, so ibwill try and get under and inspect wires connections, etc. If I find nothing, I will get a switch located.
 
Ok. So I drove the truck the last two days and didn't have any issues. It's been 60+ degrees this weekend, so that correlates with the temperature scenario. Went ahead and bought and installed a new switch.

Man, were they proud of that thing. In stock, $236 with tax and a lifetime warranty. Could have gotten one with a 1 year warranty for $85, and $10 shipping, oh and you have to prepay, oh, but it won't get here until the 4th of next month. So I just bit the bullet and got the one in stock so a could install it with the nice weather right now. Supposed to start raining tonight, be down to the 30's by noon tomorrow, then snow and highs in the 20's and low in the teens after that.

Hopefully its all good now. The upcoming weather may test my theory. Fingers crossed. Thanks again to those who helped.
 
Been a few weeks since installing the transmission switch with no issues until tonight. Did the same thing, hit neutral while in drive, tripped check engine light.

Coasted to the shoulder, shut off truck, restarted, still no go and light on.

Shifted transfer case into different positions, shifted transmission back and forth to neutral and drive while doing so to facilitate transfer case shift.

Seemed to find 4 low and drive. Shifted back to 2 high. Light still on, drove the 15 miles home.
 
Might seem stupid but have you checked the t case oil?

And have you had the trucks codes read could be a stuck solenoid in the trans.
 
I didn't pull the codes this time, but did before.
P1713 and P0700.
Seems like it was something to do with seeing the wrong pressure in reverse gear. And then a code for kicking the light on.

I need to check the transfer case fluid. That's a good idea. I will recheck the transmission, as well. I do the spin on filter on the transmission every other time I change the engine oil. So every 10k miles. I could probably stand to do internal filter at this point as well.
 

Colby`s First gen Duramax 01 lb7

So we were getting a p1711 code from the Ally... The code is stuck solenoid e , we were told by our good Mechanic buddy Lorne to change the solenoid,Pressure switch Manifold and the internal trans filter. Parts weren`t to bad 180.00 for everything we needed from the Allison Dealer. We...
ck5.com ck5.com

Look at the first 3 pages of my thread from way back. It tells of what I went though with my sons 01 Duramax.
 
max 02 said:

Colby`s First gen Duramax 01 lb7

So we were getting a p1711 code from the Ally... The code is stuck solenoid e , we were told by our good Mechanic buddy Lorne to change the solenoid,Pressure switch Manifold and the internal trans filter. Parts weren`t to bad 180.00 for everything we needed from the Allison Dealer. We...
ck5.com ck5.com

Look at the first 3 pages of my thread from way back. It tells of what I went though with my sons 01 Duramax.
Click to expand...
I will definitely look into that. Thank you.
 
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