Blinking Reverse Light (Allison Problem)

[DanB]

Hi,

I am fortunate enough to experience most of the problems with my truck while new and still under warranty. :)

My new highest priority problem is the blinking reverse light phenomenon. In this scenario, you start the vehicle and put it in reverse. Instead of just highlighting the gear for reverse, it is highlighted and blinks. You can still back up, select "D" and be on your way, but the transmission will not shift out of first gear until the truck is turned off for a minute.

Well tonight when my truck started to do this I sat there in disbelief. Not only was my truck at the shop all last week, but this was one of the problems I asked them to fix. They said they could not apply the fix unless the problem could be duplicated and verified.

While I was sitting there marveling at my lucky Sunday night, the transmission shifted. Given that the truck was in reverse and I had not done anything, I wondered what gear I was in. Tapping on the accelerator revealed ... neutral (reverse was still selected and illuminated). Out of curiosity I put the truck back into park. It shifted and everything looked normal. No lights had come on during this entire escapade.

So ... I put the truck in reverse, backed out the driveway and was pleasantly surprised to find out the transmission had no further problems.

Does anyone have any ideas on what causes this behavior and/or how to duplicate/fix it?

Dan

[FirstDiesel]

I'd consider replacing the switch on the tranny. What color is yours??? There are 2 switches,black and tan.

[dmaxalliTech]

flashing prndl is indication of trans problem. I would deff start with replacement of nsbu switch on trans. thats most likely the cause.

[Dawg]

If you do a "search" on the NSBU you should find all kinds of info. The Allison dealers sell the part for much less than the GM dealer. Several people have completed the install themselves if not on warranty.

[DanB]

Hi,

They already replaced my NSBU switch. Also, I need to be able to replicate the problem or give them a test that should fail.

Thanks,
Dan.

[77TransAm]

If it only happens right after a start up, your problem could be loss of prime. You'll find some pretty good descriptions under "converter drainback" on here - check and see if that matches your symptoms. If so, there is supposed to be a service kit released soon (if not already) that lets the dealers replace a spring or two in the front support to fix the problem.

[pinehill]

Dan,

Have you crawled under the truck to confirm that your NSBU switch was replaced?

[dmaxalliTech]

77, I have heard a fix is ready but the problem they are having is that the dipstick tube is blowing out. They still need to fix that before they release it...

[DanB]

An update:

My truck had this problem today and I drove it to the dealer. They plugged in a thinga-ma-jig and got the codes. The problem has now been documented and verified.

He said that although the Allison was a fine piece of work, the electronic interface was still young.

When my truck is fixed, I'll let you know. Thanks for everything!

Dan

[Maverick]

I've had this happen 2 times. One this week. My 3500 sat for 5 days and I started it up and let it run for 20 seconds and the put it in reverse. I coasted down my drive and noticed it was blinking. This is from the sitting so long thing. The other time is when I shift to fast from drive to reverse or the other way while snowplowing. The Allison is neat in that it won't let it slam gears. You could put it in neutral and rev it up to 3000 rpm and put it in drive. Nothing will happen. Drive will just blink. Cool.

[ 05-08-2003: Message edited by: Maverick ]</p>