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Old 05-05-2018, 05:19 PM   #1
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MD3060 weird ground issue...

I purchased a 99 Dream a few weeks ago and it had an intermittent transmission fault code... 22-16 which is the output speed sensor.

I have spent several days messing with this and have figured out my problem is some type of ground issue.

I have tested the sensor, wiring, swapped sensors with a known good sensor, run temporary new wires to the output speed sensor, etc.

I have figured out that when the Transmission ECU is unbolted from the RV, and does NOT have continuity with the chassis ground it works perfectly.

Once I bolt it back to the RV my error comes back.

I originally removed the ECU to check the pins on the receptacles more closely. I think in doing this I removed the old rusted bolts which had a poor connector making my issue intermittent.

Now my ECU has a good connection to the RV and my error only goes away when unbolted.

Any idea where to look?

I have removed and cleaned or replaced every ground connection, and wire I can find.
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Old 05-05-2018, 06:05 PM   #2
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Quote:
Originally Posted by Bleedred View Post
I purchased a 99 Dream a few weeks ago and it had an intermittent transmission fault code... 22-16 which is the output speed sensor.

I have spent several days messing with this and have figured out my problem is some type of ground issue.

I have tested the sensor, wiring, swapped sensors with a known good sensor, run temporary new wires to the output speed sensor, etc.

I have figured out that when the Transmission ECU is unbolted from the RV, and does NOT have continuity with the chassis ground it works perfectly.

Once I bolt it back to the RV my error comes back.

I originally removed the ECU to check the pins on the receptacles more closely. I think in doing this I removed the old rusted bolts which had a poor connector making my issue intermittent.

Now my ECU has a good connection to the RV and my error only goes away when unbolted.

Any idea where to look?

I have removed and cleaned or replaced every ground connection, and wire I can find.
If your error goes away when the ECU is unbolted, continuity is disrupted (no ground return); Hello. Perhaps you have a bad ECU or sensor.
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Old 05-05-2018, 08:47 PM   #3
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The sensor is in a plastic housing so I know it’s not causing a grounding issue.

It tests fine per the Allison troubleshooting manual. Ohm’s right at 300, same as the engine speed sensor. I swapped sensors with the input sensor, which I know is good, and the issue stays at the output sensor. I really am convinced this is a false error.

I am not convinced the ECU is bad either. I can find nothing wrong with it, I even opened it up to make sure I don’t have an internal grounding issue. The only place I have continuity to the case is at pin 25 in the black connector, I think, that is labeled “case ground”.

I have one more ground terminal block that’s hard to reach I need to take apart tomorrow, I hope I can access it from the top side as it will be a bear from underneath M
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Old 05-06-2018, 08:10 AM   #4
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Quote:
Originally Posted by Bleedred View Post
I purchased a 99 Dream a few weeks ago and it had an intermittent transmission fault code... 22-16 which is the output speed sensor.

I have figured out that when the Transmission ECU is unbolted from the RV, and does NOT have continuity with the chassis ground it works perfectly.

Once I bolt it back to the RV my error comes back.
Check out the post below. Sounds like a similar problem.

Known Allison ECU Grounding Problem

FWIW
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Old 05-07-2018, 08:51 AM   #5
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sounds like you need the ECU isolation kit 29535576
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Old 05-07-2018, 06:46 PM   #6
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If I remember correctly, the TCM (transmission control module) gets power directly from the VIM (vehicle interface module). The VIM is supposed to have dedicated positive and negative wires that come directly from the chassis battery. A positive wire from another terminal that feeds other systems, or a ground strap wire from the chassis is not acceptable. This is very important for proper operation of the transmission. Don't ask me exactly why this is true, but the troubleshooting manual gives specific instructions about where power is drawn from for the computer.

I went through all of this on our rig over the last couple years. There was a bad power supply in the TCM which I had replaced at Transmission Instruments. After fixing that, I still had issues. I discovered that the positive wire from the battery had been cut, and someone went to the extent of jumping a switched ignition source to power the VIM. You wouldn't think this to be a big deal, but it wreaked havoc on the shift points. Once it was wired correctly, everything started to smooth out, and the 35-00 error that i had seen from day one finally went away. Not saying this is your problem, but maybe it's something to consider.

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Old 05-08-2018, 05:09 AM   #7
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Thanks for the replies guys.

I seem to have clean power at the ECU but thats not saying i still don’t have an issue with the VIM I guess.

The only way i seem to have solved this issue, i hope, is by isolating the ECU from the chassis ground. After doing so I have gone through about 10 restarts in the shop without an error code coming up. I still need to test drive it however.

I hope this at least gets me by until whatever is giving me issues fails more completely and simplifies the troubleshooting process!
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