Sunday, October 14, 2007

Allison Automatic Transmission Wiring & Troubleshooting

The Allison Transmission Control Unit on the 1999 Saf-T-Liner is located under the floor directly below the driver. There are 3 plug-ins which is an easy way to tell this is a W-TEC 3 system [World Transmission Electronic Unit 3rd generation]. The Transmission vehicle speed signal enters here and exits at two different plugs, one for the speedometer and the other to the Cummins ISC ECU.

We will trace the exiting wire from the ECU that provides our Vehicle Speed Signal since that is the code and the speedometer is operating normally. Since we have speedo operation that gives us an obvious clue that the incoming signal to the Trans ECU is OK.[resistance should be checked regardless]
The wire we want to trace goes from the Trans ECU to the VIM [Vehicle Interface Module]
Removing the dash back cover makes this check MUCH easier.

Remove the cover from the VIM

The VIM is an interface between the Trans ECU and the chasis wiring. Various operations are accomplished through this module like the exhaust brake, back up lights, neutral start, high idle and of course our vehicle speed signal runs through here to the Engine ECU.
[Click the Pic to Enlarge]
Now we can check the continuity and see if we have a circuit. After checking this out there is no connection between the Trans. ECU and the VIM.
I'll run a new wire to repair the open circuit, an easy fix. It's nice to get a gimme once in awhile!

In the VIM you'll notice a series of relays and 2 fuses. If you experience a dead keypad and there is battery voltage to the VIM then check these fuses. One is main power & the other is ignition power.

The other vehicle speed signal wire [tan wire # 157] comes from the trans ECU directly to the speedo. The speed signal to the VIM is the same number [tan wire #157] since it comes from a different plug.

This is where it all begins from the output shaft housing of the transmission. The output sensor is a single coil unit that sends an AC voltage to the Trans ECU.
There is a toothed wheel rotating inside the housing that creates the signal to the sensor.
The Allison 3000 Automatic Transmission is a very reliable unit when maintained properly. The wiring problems come and go but are easy to trace and repair with the right tools and wiring diagrams.


Gary said...

Just wanted to pass a quick thank you for helping me fix our 2000 Bombardier snowcat. In your 2005 blog you covered bleeding the fuel system on the 8.3 and got me up and running in no time.

Thanks again
Whistler Bc Canada

John Whelan said...

Your Welcome Gary,

You'll need to be prepared for the 2010 Olympics.

Good Luck!

Steve Polhill said...

John I have a question. I have a 1994 Winnebago Diesel pusher with a 6 speed Allison Trans. It's worked flawlessly for the 4 years I've owned it. But last week I went out to starting to bring it inside and it won't start and I have a blank screen on the trans selector panel. The engine will start if I jump the starter, and shuts off with the key, but it won't go into gear I have igniton and start signal at the VIM the two 10 amp fuses in the VIM are good. I was wondering if you had any suggestions. could the VIM be bad? It worked perfectly about a month ago.

Phillip Swart said...

Hi John. Wonder if you can help me with Allison 3500 WTECIII. Its in a Volvo Busscar. The Engine is cutting out as you approach a stop with your foot on the brake pedal. I suspected the lock up f solenoid. The valve body was removed and currently inspecting it but nothing seems out of place. I found one DTC that had to do with engine coolant temperature and sometimes communications. I believe the controller communicates via can with the engine ecu??
Thing is the coms connector 3 pin isnt connected to anything. Is it possible that communication problem with engine ecu can cause that problem. Or is it possibly the lock up mech within the torque converter. Phillip

John Whelan said...

The trans should log a code if solenoid is faulty. We had trouble with low rpm at idle causing a stall in gear and also within our fleet the engine shutdown system detecting low oil pressure on a Cat 3116 diesel which was caused by a weak engine oil pump.

William Harrison said...

I have a problem with an 03 Beaver marquis. After sitting for 2 months it would not start (not attempt to turn over) I installed a rear start switch and can get the engine running. Now my shift panel is dead. Both fuses in the Allison vim are good.
The transmission is an mh4000. If I had a wiring diagram of the vim I could (hopefully) trace the problem.

John Whelan said...

Check your battery voltage. The trans needs direct battery feed to operate the shift pad and VIM

S said...

Hello. My name is Sandra & I’m the typer….my husband is Dave. I’ve been reading your blog for awhile and it’s been helpful on several occasions. Thanks. We have a 1993 Monaco Dynasty. Cummings 300hp engine. Allison MD3060. Rig drove fine until a few weeks ago. Problem: While driving Key Pad for tranny would flash and go black. Then no ability to put the rig in any gear. Turned the engine off. When Dave cranked it back up the Panel worked again. Then last week the panel started flashing and going black every time we cranked it up. Turning engine off & on ceased “fixing” the issue. So Dave inspected all the sensors/inputs going into the transmission. With engine off when he unplugged then replugged the engine speed sensor then started up the engine the control panel would work for a few minutes...then begin flashing...then go black. A few times it worked long enough that we were able to drive the coach forward, back it, turn it around in our driveway. Soon afterwards the plugging/unplugging stopped working. Tried dielectric grease. Nothing. Installed a new engine speed sensor which resulted in the flashing key pad situation again, followed by black- nothing. Today we replaced the two prong electrical connector that the engine sensor plugs into. Now the key pad flashes....stays on a few seconds....flashes sporadically...goes black...flashes...stays on....flashes..goes black, etc. I did notice during the flashing a 0 would sometimes we displayed. also...The DO NOT SHIFT light is on when the key pad goes black. Dave also noticed that that intermittently the tack doesn’t work at idle but as soon as he revs the engine it kicks on.
Any thoughts or suggestions you can send our way would be much appreciated. We're conundrafied. THANK YOU…Sandra & Dave in Texas.