Allison tranny issue

First check for low voltage-- the transmission ECU can to some really "stupid" things if it has improper voltage.

Next, check the transmission for stored codes. VERY easy.

Ignition on, engine off:
Push the transmission shift pad up and down arrows at the same time. On your 1994, that should bring up d-1 (for diagnostic code 1). It will be followed by two two digit codes. If you get d-1 - -, there are no stored codes. If you to get a d-1 and code, push the mode button to bring up d-2. Continue until you get a d- (some number) and - - .

Push N and turn off the key.
Let us know what you find.

Another suggestion is to unplug and replug the ECU and shift pad. A loose connection can cause issues as well.

Also sounds like the exhaust brake program that does an auto downshift when the throttle is 0(zero) with EB on.

Jim

Jim-Linda wrote:
Also sounds like the exhaust brake program that does an auto downshift when the throttle is 0(zero) with EB on.

Jim

Agree, that could be it, but have NEVER seen a 3rd gear pre-select for the exhaust brake. 2nd and 4th are common. Yes, any gear can be programmed.

BUT, the flashing "6" says there are electronic issues!

Well, I got the coach back today and checked the error codes stored. They were:

56_22 2nd range verification test
25_11 Output speed sensor @ 0 rpm, 1st
54_12 Oncoming ratio test 1 to 2
69_32 This code doesn't exist in the Allison manual I found online

I cleared them and drove it.

The transmission shifting was a little rough overall I thought and sure enough, when I got on the highway and slowed a little the display lit "3" and the DO NOT SHIFT light popped on. I pulled over and got the codes.

56_55 5th range verification test

I started again and soon had the same issue, only this time the display lit a "6". Codes from that:

56_55 5th range verification test
56_22 2nd range verification test

Then it drove the rest of the way home ok.

Does that mean anything to anyone? I'm going to look around for an Allison place near me (Waverly, IA)

They have a Harrison Truck Center near me - anyone have experience with them?