MD3060 issues

[Mat7783]

Had 6th gear unlocked 2 years ago and all was good until this week.my Md3060 display is blanking out for a second ,then comes back on at 6 for 6peed operation.setting it to 5 or 4 when traveling at slower speed still resets back to 6 and tranny jolts during this process as it is losing communications with TCM?seems to more consistent over bumps in the road.checked cabling from tranny to TCM and do not see any signs of corrosion.is my first step to replace tranny fluid and filters!

 

[ewo1]

Last year I had a scary situation with my factory opened 6 spd bus, it felt like the TCM was resetting itself causing a "jolt/kick" when switching gears. Only did it from a stop or a slow down, downshift then upshifting.

My issue turned out to be that the blade fuse holder in the battery box, one leg was overheating. You could visibly see one leg was darker than the other.

I cut out the fuse holder and replaced it with a new one, fuse too, problem solved.

Post #17 of this thread and you can see a pic of what my fuse holder looked like.


quick advice, Check your fuse holder....

 

[Omnibot2000]

Had 6th gear unlocked 2 years ago and all was good until this week.my Md3060 display is blanking out for a second ,then comes back on at 6 for 6peed operation.setting it to 5 or 4 when traveling at slower speed still resets back to 6 and tranny jolts during this process as it is losing communications with TCM?seems to more consistent over bumps in the road.checked cabling from tranny to TCM and do not see any signs of corrosion.is my first step to replace tranny fluid and filters!

Not an oil and filter problem from my experience but if it's due or looks/smells well used then change it.

As mentioned, check your power supply ( fuse and holder) You may have to start back probing power supplies checking for voltage drops. Very least, check system voltage going to your electrical with a scanner.

I had those key pads blank out on me for a Sterling truck. Took me a full day but had the harness opened up between the controller and the TCM to find wires had been stab tested resulting in a corroded power supply as well as a number of signal wires in one section of the harness from a previous repair.

 

[cadillackid]

Not an oil and filter problem from my experience but if it's due or looks/smells well used then change it.

As mentioned, check your power supply ( fuse and holder) You may have to start back probing power supplies checking for voltage drops. Very least, check system voltage going to your electrical with a scanner.

I had those key pads blank out on me for a Sterling truck. Took me a full day but had the harness opened up between the controller and the TCM to find wires had been stab tested resulting in a corroded power supply as well as a number of signal wires in one section of the harness from a previous repair.

just fixed a heater on a friends car where the underhood wires had appeared t ohave been backprobed at some point.. where they smushed the rubber seal of the GM weatherpak connector in im guessing to get a meter lead in ..allowed water over time.. took out the blower speed control unit from the corrosion and could see where the terminals had arc'd. somewhat older cadillac with fully variable speed heat / AC motor...

 

[Omnibot2000]

just fixed a heater on a friends car where the underhood wires had appeared t ohave been backprobed at some point.. where they smushed the rubber seal of the GM weatherpak connector in im guessing to get a meter lead in ..allowed water over time.. took out the blower speed control unit from the corrosion and could see where the terminals had arc'd. somewhat older cadillac with fully variable speed heat / AC motor...

If you don't use the proper tooling to back probe a connector you will destroy the seal or render it useless on keeping it weather tight.

 

[cadillackid]

when I used to do a lot of work on the 80s / 90s GM vehicles I made tap-in pigtails for all the common weatherpak connectors.. nowadays there are hundreds of different connectors used so wouldnt be feasible anymore to make test harnesses..

 

[Omnibot2000]

when I used to do a lot of work on the 80s / 90s GM vehicles I made tap-in pigtails for all the common weatherpak connectors.. nowadays there are hundreds of different connectors used so wouldnt be feasible anymore to make test harnesses..

Totally agree.

Taps now come in the form of thin filament wires that slide between the wire and the seal to reach the crimped portion of the pin to perform the test.

Hacks out in the field will take there probe and just jam it in the backside of the plug with no regard to the seal. At that point, just pierce the wire if you wanna half a$$ it.

 

[Mat7783]

Fuse holder

My in-line cheap Chinese fuse holder does not hold the 30amp fuse securely in the socket.comes loose in my hand.so I replaced it with an inline 30amp circuit breaker to see if issue clears.

 

[ewo1]

My in-line cheap Chinese fuse holder does not hold the 30amp fuse securely in the socket.comes loose in my hand.so I replaced it with an inline 30amp circuit breaker to see if issue clears.

The tcm fuse should be 10 amps, not 30 amps!
Correct that…

For some good reading take a look at this thread-> https://www.skoolie.net/forums/f9/allison-keypad-dead-43353.html

Another item very rarely talked about is the VIM unit.
Several relays in there that if something went bad here, it would affect tranny ops. Don’t focus on that just yet.

Focus on a new, expensive and high quality fuse holder… and clean grounds.

 

[Mat7783]

So my bus came with the 30amp in-line fuse on the positive battery lead.i just read that I should have 2 10amp fuses ,one for TCM and other for VIM.where is the VIM usually located? My TCM is under the driver’s front bumper area.Thomas bus ER

 

[ewo1]

So my bus came with the 30amp in-line fuse on the positive battery lead.i just read that I should have 2 10amp fuses ,one for TCM and other for VIM.where is the VIM usually located? My TCM is under the driver’s front bumper area.Thomas bus ER

Sent you a PM !

 

[Mat7783]

So my update on my MD3060 issue was a simple fix,thankfully.replaced Chinese inline fuse holder with a new Chinese inline fuse holder along with a inline circuit breaker used as a switch so I do not have to remove fuse while bus sits idle for more than a week .this was being done to prevent any possible parasitic drain.problem solved after 5 hour trip without a single hiccup.tranny control pad behaved beautifully

 

[Mat7783]

Thanks to Ed (EWO1) for the info and time.