allison md3060 and non-functioning exhaust brake

[Sierra_Valley_M]

I have searched this site and searched and posted this issue on another site.

Here's the problem:

We have a 1992 Monaco Dynasty with an Allison MD 3060 transmission, a mechanical 6CTA 8.3 Cummins motor and a Jacobs exhaust brake. Several months ago the exhaust brake became erratic and then not operating. I have done the following:

1. Checked the throttle switch to make sure it is functioning and the brake itself.
2. Changed and added a spring per Cummins.
3. Changed all of the relays in the Vehicle Interface Module (VIM).
4. Cleaned all of the connectors to the Allison ECU.
5. Checked voltages at the ECU per John at Transmission Instruments.
6. Cleaned and reconnected all grounds in the dashboard and front run panel.
7. I had some codes on the key pad.
d1 = 3500, power interrupt
d2 = 3414, power interrupt, block check sum
d3 = 2112, Throttle Position Sensor (TPS) below low
d4 = --
d5 = --
8. The power interrupts were due to a cheap screw type switch on the ground side of the chassis battery. (Since removed)
9. Took the MoHo to an Allison repair shop which is very thorough and professional. They installed a new TPS and we went for a test drive with their computer connected. The brake worked perfectly. I started home and tried the exhaust brake, it didn’t work. As it was after hours I continued home.
10. Took the MoHo back a couple of days later and when their computer was hooked up for another test drive THE BRAKE WORKED PERFECTLY. The service manager and the tech had not seen this before.
11. Removed, cleaned and checked the resistance of two speed sensors on the trans.
12. The exhaust brake will work once in a while, not much, and only after about 10 to 30 seconds after I activate the switch on the dash.
13. Replaced and soldered all connectors direct from ECU to Battery. No change!

Mike

[wolfe10]

Thanks for posting the solution.

Yes John is THE Allison electronics guru!

[Sierra_Valley_M]

Solved! I posted this on another site also in the event that if someone has a similar issue they might do a search and find some information.

The exhaust brake now works perfectly! I sent the ECU (Electronic Control Unit) to Transmission Instruments in Flower Mound, Texas and they repaired the ECU WTEC II including the power supply. The cost was much lower that purchasing a new unit. $495 plus shipping instead of several thousand dollars. After chasing the many exhaust brake fixes for quite a while I became aware of the exhaust brake functioning ONLY when the trans was hooked up to an Allison diagnostic computer.

The problem has finally been fixed thanks to John and Judy Kopalek at Transmission Instruments. Transmission Instruments

[Sierra_Valley_M]

wolfe10 wrote:
So, tell us how far into the "exhaust brake cycle" you get when this failure occurs:

1. Does the Allison shift pad left window go from "6" to your exhaust brake pre-select gear (can be anything, but "2" and "4" are most common)?

2. Does the transmission start downshifting toward the pre-select gear?

If both of the above happen, my next move would be to temporarily wire a voltmeter or even test light to the exhaust brake solenoid to see if it is being activated.

The trans will go to 2nd when and if it activates and powering the exhaust brake solenoid with 12 volts works. The thing that seems to be the problem is why the brake works perfectly when the Allison computer is hooked up to the data port. Bad connection to the ECU?

There have been no codes since the TPS was replaced.

Thanks for your help!

Mike

[RLS7201]

I think "d3 = 2112, Throttle Position Sensor (TPS) below low" is a clue.
I've seen and repaired a similar problem.
Check the throttle linkage at the engine. There is a shaft and linkage that connects the throttle cable and the TPS cable. The shaft and linkage may be worn to the point of failure. It could cause erratic failure. That was causing TPS error codes on my customers 8.3 mechanical Cummins.

Richard

[wolfe10]

So, tell us how far into the "exhaust brake cycle" you get when this failure occurs:

1. Does the Allison shift pad left window go from "6" to your exhaust brake pre-select gear (can be anything, but "2" and "4" are most common)?

2. Does the transmission start downshifting toward the pre-select gear?

If both of the above happen, my next move would be to temporarily wire a voltmeter or even test light to the exhaust brake solenoid to see if it is being activated.

[rcmiller32]

Check the linkage and solenoid on the exhaust brake. Could have binding or a solenoid going bad. Also check the wiring from the exhaust brake.

[Ivylog]

And you expect us to have a answer? Other than buying a newer MH I'd bypass everything getting down to a on/off switch, maybe a throttle switch, and a wire to the exhaust brake solinoid. You will have to manually down shift the tranny.