Allison AT NSBU switch problem

Ray,IN · 03-17-2006, 10:15 AM

My '02 D/A sat for a month without being moved after I had heart surgery. When I was able to drive again, the truck would not move in any gear, and the service engine soon light was on. I sat and ran the engine at 1,500 RPM for about 10 minutes with the AT in neutral, and the transmission then would shift into any gear. I phoned my local Chevy dealer, and the diagnosis was a faulty NSBU switch on the Allison AT. The switch is not sealed properly and allows water to corrode the wiring. This is a known problem for the 2001-2003 Allison AT's. GM issued a TSB on this problem, and even though my truck is past warranty the dealers replaced the switch as a courtesy warranty. The new improved switch is water tight to prevent re-occcurance. I hope my experience helps.

Ray,IN · 04-09-2006, 07:45 PM

UPDATE: Well, with the new switch the problem has returned, intermittently. That is the problem, the Chev dealership service manager says since the "service engine soon" light goes out after the truck is warmed up he must wait until the light is on when his technician reads the computer, or they can do nothing. The problem occurs when the truck sits for over 4 days in a cold, humid climate, and I can't let the dealer have the truck to just sit for 4 or more days for the light to come on.

April 11, 06 UPDATE: Well, my truck is at the GMC dealership, the Chevy dealer did not have a certified Allison AT tech. Now they say the drain-back valve in the front pump is defective and must be replaced. The AT, and TC must be removed to access the front pump and replace the valve.Thank goodness GM is performing the work under warranty, because they know this is another problem with the Allison AT and had issued a TSB detailing the fix.

CapeAce · 04-16-2006, 05:42 AM

Actually the NSBU switch falls under the 100k emissions warranty, don't why it is, but atleast their covering a problematic part.

Ray,IN · 04-16-2006, 06:20 PM

Truck repaired and on the road! GM warrantied the entire cost.

Ericjeeper · 06-07-2006, 02:08 PM

My dually 50 k miles on it has been at the dealership for three days now.. I took it in because of the hesitation after sitting over night in the garage. it does not always slip, and oif course they can not duplicate the scenario.
There was a leak that started saturday, I figured another rock had hit the spin on oil filter. but not it was fine fluid was not coming from that item.
I have an extended warranty so i took it in. They said it was the shift shaft seal that was leaking. so they ordered the part. well lo and behold the leak was above that, coming from a vent he said.. The service tech called me and asked what I haul or tow with the truck. I replied.. well wife drives it to work and occassionally she hauls some very heavy groceries in the back. LOL
and it has not had a trailer hitched to it in six months and that was either the 31 foot airstreamTT or the car hauler with the jeep sitting on it. Neither of which go over 8k. so basically he told me he has no idea why the fluid has ran out the vent.he said it must have been hot.. I have towed up mountains and all over the west towing the airstream and never once in 90 plus degrees did it ever get near 200 even. so I doubt hauling groceries it overheated.
Could my problem be the same as above?Thanks in advance..

**Monster truck** · 06-07-2006, 05:22 PM

is there any body else that is having trouble with there alisson?

Mike L. · 06-08-2006, 07:35 AM

Ericjeeper
I often see fluid come out the Ally vent and it only happens when the trans is over filled. Fluid level must not show over the HOT full mark on the stick. Preferably a quarter inch below.

Ray,IN · 06-08-2006, 06:40 PM

ericjeeper, I suspect you have a switch problem also. When its intermittent like that have the tech read the codes in the computer. Late model Allison's don't have a NSBU switch I"m told. It that case its another problem entirely. Once I had an AT rebuilt while traveling, at an AMCO shop. They did an excellent job, before I left the shop manager said the AT was a pint low and to leave it that way. He said years of experience had proven to him that AT's that were used in extreme conditions, like police cars, ambulances, motor homes, etc. experienced over-full fluid levels. This is much harder on an AT than thought possible. They had been running these vehicles a pint low for several years without problems. GM issued a TSB for the NSBU switch, it may be viewed diesel-central.com. Scroll to the bottom of the TSB page for GM. Click on the lower TSB link.