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Old 02-01-2025, 11:00 PM   #1
Skoolie
 
Join Date: Dec 2019
Location: Sanford Florida
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Year: 2000
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Chassis: MVP/ER
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MD3060 issues

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!

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Old 02-02-2025, 09:17 AM   #2
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Join Date: May 2015
Location: Central Tx.
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Year: 1999
Chassis: Amtran / International
Engine: DT466E HT 250HP - Md3060
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....
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Old 02-02-2025, 08:47 PM   #3
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Join Date: May 2023
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Originally Posted by Mat7783 View Post
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.
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Old 02-03-2025, 08:12 AM   #4
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Originally Posted by Omnibot2000 View Post
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...
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Old 02-03-2025, 08:29 AM   #5
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Originally Posted by cadillackid View Post
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.
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Old 02-03-2025, 10:38 AM   #6
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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..
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Old 02-03-2025, 10:50 AM   #7
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Join Date: May 2023
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Originally Posted by cadillackid View Post
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.
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