HELP! STRANDED! - Allison B500 Keypad Dead...

mqbus767 · August 21, 2024, 03:25:40 PM

Hello Bus Nuts,

I'm currently 10 miles outside Springfield MO off I-44 at Hood's Truck Center with a broken down bus. We were driving on the highway when all of a sudden the bus would not accelerate beyond about 40MPH. I also noticed at the same time the spedometer wagging back and forth. I was able to limp off the interstate and pull into the truck center. I noticed that the Allison keybad (WTEC III) was not illuminated. I shutdown the bus and began some troubleshooting, but found nothing out of the ordinariy. I've checked all ECM fuses and the WTEC fuse; all good. I checked and swapped some relays in the front J box, but nothing changed. I don't think the relays have anything to do with it from the labels. The bus will not start.

The transmission was quite a bit low on fluid so I'll be adding more, but from all my research a low fluid level should not cause the keypad to go dead. I pulled the keypad apart and verified that the circuit board is getting 24V.

At this point I'm sending the family back to Houston in a rental car while I remain with the bus to get it fixed/recovered. I've located a couple of keypads at various and extortionary prices, but I'd really like to know for sure it's the keypad before I invest in that ebay purchase.

Any ideas or help would, as always, be much appreciated!

freds · August 22, 2024, 09:11:56 AM

On my bus when the speedometer was wagging back and forth the power line to the meter was not hooked up. (partial dash conversion by a previous owner.)

I believe that is an electronic transmission so a loss of power would inhibit it's ability to shift.

Glennman · August 22, 2024, 01:19:20 PM

Some of my gauges on my dash wagged back and forth when my starting batteries were low, but I don't recall which gauges. Once I replaced the battery with the dead cell, everything went back to normal. Maybe a battery and/or alternator (low power) problem is causing all this??? Only a guess!

mqbus767 · August 22, 2024, 01:43:15 PM

I checked the battery voltages and they are 12.8 and 12.9, so I think they are OK. Everything else on the bus seems to work OK. The gauges sweep when I power up the bus, but the keypad gear seven-segment display is black and the start button does nothing.

mqbus767 · August 22, 2024, 03:31:36 PM

I found a place in Springfield that will bench test the keypad and TCM. Crossing my fingers that it's the keypad.

mqbus767 · August 23, 2024, 11:11:15 AM

Uber'd to Central Power Systems and Services in Springfield with my keypad and transmission ECU. They bench tested the ECU but could not get it to connect. The tech there was pretty confident the ECU is dead. I was able to locate a used one for sale from Fowler's Autowrecking with a 6 month warranty. It's being shipped to me and should be a plug-in replacement. It's not a 100% guarantee that the ECU is programmed the same as mine, but the CIN and other numbers do match. I called Fowler's to explain the situation and it sounds like I should be able to just plug it in and go. Stay posted!

luvrbus · August 23, 2024, 03:41:17 PM

They all have the same perimeters even if the programing is not the same you can toggle the right perimeter with a Pro/Link ,you should have gotten a cat eye on the pad with a bad ECM you may have a dead pad too lets hope not .One has to love the 3 to 5k electrical glitches

mqbus767 · August 23, 2024, 05:23:42 PM

As a part of the bench test they connected a known-good keypad; no cat eyes, no nothing. We shall see...

luvrbus · August 24, 2024, 03:11:59 AM

Quote from: mqbus767 on August 23, 2024, 05:23:42 PM
As a part of the bench test they connected a known-good keypad; no cat eyes, no nothing. We shall see...

Save your TCM they have a fuse and backup battery inside the module you may get lucky and have a spare for a few bucks

mqbus767 · August 24, 2024, 05:44:01 PM

With nothing but time on my hands, I went ahead and opened the ECU. The burnt electronics smell was strong and I located a blown transistor. It got pretty hot because it scorched the IC on the opposing board. I don't have a circuit board schematic, so I'm not sure what the transistor was driving. I guess my fear now is that whatever device is connected to that/those pin(s) is shorted and could(?) be blowing the transistor. My gut tells me that surely Allison has some sort of dead short protection on this ECU, but who knows.

Does anyone have any experience with the internals of the WTEC III ECU? Does anyone know of a shop that remans them and might be willing to look at a few pictures for me?

luvrbus · August 24, 2024, 06:40:37 PM

I have the rare principals of application manual, if i get time Sunday will check and see if it in it, probably does it has a ton of fold out pages covering the WTlll electrical and hydraulics

Van · August 25, 2024, 07:21:28 AM

Looks pretty smoked. Over voltage possibly?

mqbus767 · August 25, 2024, 02:32:05 PM

I think an overvoltage on the TCU is less likely, but possible.

In my searching, I found an RV owner that had a similiar thing happen on his rig. A cap smoked on his board. He seems to have had more moving parts than I did with the storage facility moving his rig. Interestingly his TCU seems burned up in almost the same spot as mine:

https://www.youtube.com/watch?v=Lx80avW6s24

mqbus767 · August 26, 2024, 11:46:13 AM

Just heard back from a tech at Transmission Instruments (https://www.transmissioninstruments.com/).

Quote"Hi,

Yes this is a common failure in the WT3ECU909 & WT3ECU910 models. In all the cases I've seen this is a internal failure not caused by something on the vehicle.

"

So that gives me a boost of confidence that I'll be able to swap it out without immediately blowing the reman. Now the only remaining question is about programming. I told Fowler's exactly which drive train/bus I have and they should have shipped me a TCU from the same setup. Hopefully getting closer to getting her patched up.

Van · August 26, 2024, 12:44:10 PM

Good news indeed. Here's to getting back on the road soon!