M1078 Transmission Problem

[Satchaser]

Hello Friends.

I bought a 1995 M1078 from GovPlanet last year. 10k miles. Great truck, it ran right off the start. No leaks, everything seems to work except the CTIS which I think is just unplugged. I have put about 200 road miles on it, and as I said it performs perfectly. Engine starts instantly and runs smooth.

Last weekend I was on the road (paved) doing about 50 when I lost power, as if the truck went into neutral. Engine was fine, Transmission display seemed fine (but I was distracted getting off the road with no power). I shut down and restarted with no effect. I got lucky that I was only 1000 feet from home so a quick tow.

I read through the posts of SS and nothing seems to be right on target. I have modest mechanical skills. I physically inspected the transmission and nothing looked loose or out of place. No marks, no fluid marks, etc.

I checked the Tranny fluid levels, a bit low so I topped it up (15w40).

I have restarted the truck several times, it *feels* like the transmission is just not getting the command to shift into any gear (Reverse, Drive, Mode, etc.), all are non responsive. I should note that at startup the display looks normal. If I push D I get 7 2 displayed, but I do not feel the transmission engage, and if I push the accelerator the engine will rev up, but you feel no tension from the transmission. After a few changes of gear selection, the display will stop responding to change gear commands, however it will respond to commands such as 'show error log'. I can post a video if anyone thinks it will help.

I checked the codes on the Tranny display and here are the results:

D1 25 11 (Output speed sensor, detected at 0 output rpm, 1st)
D2 55 17 (Oncoming C3PS test (after shift), 1 to R)
D3 56 66 (Range verification ratio test, 6th)
D4 21 12 (Throttle position sensor, failed low)

I do not know how old some of these are, I can only verify that D1 25 11 is new (It was D2 the first time I looked at the log)

I am hoping one of you recognizes the issue or has a good recommendation for a mobile tranny mechanic in Sonoma County California.

Thanks and let me know what other information would be useful.

 

[NDT]

For sure all the 25 XX codes inhibit shifting so that is why you see that. Here is the troubleshooting guide if you don't have it. Dig in, you might figure it out without dropping huge coin on an Allison guy.

 

[Satchaser]

Thanks for the guide. I will start on it.

 

[coachgeo]

check your flywheel bolts thru the port hole on bottom of bell housing

 

[Third From Texas]

check your flywheel bolts thru the port hole on bottom of bell housing

That would be a LOT of bolts to come lose at once.

 

[Satchaser]

Just curious, about how many bolts are there on the flywheel?

 

[Ronmar]

since you have documented them you can clear the codes in memory and see if there are any hard/current faults. The display showing (Mode On) while a D memory position is being displayed indicates a current active fault...

 

[Skyhawk13205]

Hello Friends.

I bought a 1995 M1078 from GovPlanet last year. 10k miles. Great truck, it ran right off the start. No leaks, everything seems to work except the CTIS which I think is just unplugged. I have put about 200 road miles on it, and as I said it performs perfectly. Engine starts instantly and runs smooth.

Last weekend I was on the road (paved) doing about 50 when I lost power, as if the truck went into neutral. Engine was fine, Transmission display seemed fine (but I was distracted getting off the road with no power). I shut down and restarted with no effect. I got lucky that I was only 1000 feet from home so a quick tow.

I read through the posts of SS and nothing seems to be right on target. I have modest mechanical skills. I physically inspected the transmission and nothing looked loose or out of place. No marks, no fluid marks, etc.

I checked the Tranny fluid levels, a bit low so I topped it up (15w40).

I have restarted the truck several times, it *feels* like the transmission is just not getting the command to shift into any gear (Reverse, Drive, Mode, etc.), all are non responsive. I should note that at startup the display looks normal. If I push D I get 7 2 displayed, but I do not feel the transmission engage, and if I push the accelerator the engine will rev up, but you feel no tension from the transmission. After a few changes of gear selection, the display will stop responding to change gear commands, however it will respond to commands such as 'show error log'. I can post a video if anyone thinks it will help.

I checked the codes on the Tranny display and here are the results:

D1 25 11 (Output speed sensor, detected at 0 output rpm, 1st)
D2 55 17 (Oncoming C3PS test (after shift), 1 to R)
D3 56 66 (Range verification ratio test, 6th)
D4 21 12 (Throttle position sensor, failed low)

I do not know how old some of these are, I can only verify that D1 25 11 is new (It was D2 the first time I looked at the log)

I am hoping one of you recognizes the issue or has a good recommendation for a mobile tranny mechanic in Sonoma County California.

Thanks and let me know what other information would be useful.

I would suggest checking the ohms of your speed sensors. Your codes 55 56 and 25 give an indication of a speed sensor issue. The tranmission controller knows the correct ratios of the speed of the input vs output. If the input and output ratio is out of range or non existent it may give a neutral no clutch response. It could be slipping clutches or a bad sensor. Good luck

 

[Suprman]

Output speed sensor is usually the engine output speed. Its a common failure item. Its a small inexpensive sensor on the bellhousing and held on by a small bolt. Maybe the connector just fell off. Or it could be a wiring harness issue. Take the grill off. The trans harness meets the cab drivers side on the hump. Look for dry cracked insulation coming off. You didnt recently pressure wash the truck? I also see low voltage issues causing trans problems. Lousy main ground I add one from the batt negative to the main frame rail? Water dripping down over time can get into transmission control components and cause issues.

 

[Coffey1]

What i am thinking bad throttle senser

 

[Third From Texas]

That's not a transmission problem.

THIS is a transmission problem !

;p


;p

 

[Satchaser]

Output speed sensor is usually the engine output speed. Its a common failure item. Its a small inexpensive sensor on the bellhousing and held on by a small bolt. Maybe the connector just fell off. Or it could be a wiring harness issue. Take the grill off. The trans harness meets the cab drivers side on the hump. Look for dry cracked insulation coming off. You didnt recently pressure wash the truck? I also see low voltage issues causing trans problems. Lousy main ground I add one from the batt negative to the main frame rail? Water dripping down over time can get into transmission control components and cause issues.

I did not recently pressure wash the truck or do anything else that would disturb the bottom. I did have an issue with two of the older batteries and they were low. This was just before the final drive. After the problem I did ensure that the batteries were fully charged, but I am suspicious of their quality. The two other batteries are just a few months old. The volt meter is in the green, and the engine has no hesitation to crank when starting.

Does anyone happen to have a link to the Output Speed Sensor that @Suprman mentions? Is it this?

Allison 29536408 Transmission Speed Sensor

Check out the deal on Allison 29536408 Transmission Speed Sensor at XDP

www.xtremediesel.com

 

[Skyhawk13205]

I did not recently pressure wash the truck or do anything else that would disturb the bottom. I did have an issue with two of the older batteries and they were low. This was just before the final drive. After the problem I did ensure that the batteries were fully charged, but I am suspicious of their quality. The two other batteries are just a few months old. The volt meter is in the green, and the engine has no hesitation to crank when starting.

Does anyone happen to have a link to the Output Speed Sensor that @Suprman mentions? Is it this?

Allison 29536408 Transmission Speed Sensor

Check out the deal on Allison 29536408 Transmission Speed Sensor at XDP

www.xtremediesel.com

Take out your keypad/ecu then ring the runs for the turbine and output speed sensors for the correct range. If not in the range it should just be a sensor/wiring repair. For parts I suggest going to an Allison dealer, it may be the same price or a little more expensive but they should have the correct/updated parts. You can cross reference with the TM parts manual as well.

 

[Satchaser]

I did not recently pressure wash the truck or do anything else that would disturb the bottom. I did have an issue with two of the older batteries and they were low. This was just before the final drive. After the problem I did ensure that the batteries were fully charged, but I am suspicious of their quality. The two other batteries are just a few months old. The volt meter is in the green, and the engine has no hesitation to crank when starting.

Does anyone happen to have a link to the Output Speed Sensor that @Suprman mentions? Is it this?

Allison 29536408 Transmission Speed Sensor

Check out the deal on Allison 29536408 Transmission Speed Sensor at XDP

www.xtremediesel.com

I searched this forum and found a post from @Dave21 that points to part number 29505601. I'll work with that unless I hear otherwise.

 

[Satchaser]

Take out your keypad/ecu then ring the runs for the turbine and output speed sensors for the correct range. If not in the range it should just be a sensor/wiring repair. For parts I suggest going to an Allison dealer, it may be the same price or a little more expensive but they should have the correct/updated parts. You can cross reference with the TM parts manual as well.

Thanks a ton for this.

 

[Satchaser]

I have visually inspected the wires and harness. Nothing looks stressed or warn. The sensors look unscathed and in good condition. I have not gotten to ohm'ing out all of the wires as suggested.

Two new ideas have arisen:
1) Once the engine is started, the transmission will not attempt to go into gear. Would the speed sensors really be relevant since the speed is at 0? If I rev the engine, while in gear, after a bit, I do get the 25 error. This makes me think that the sensors work as it is true the engine is spinning but nothing is coming out of the transmission.
2) A local mechanic, who is good with Cat's but admitted he knows little about Alison's mentioned the one thing he has seen is that the ECU(??) has a dedicated power lead from the batteries and if its not perfect problems happen. This struck a chord because prior to the problem I was monkeying with the batters to charge the older ones.

Here are my current questions.
1) Does the shift selector get its power from the ECU? Given that it lights up, does this mean that the ECU is getting power (perhaps voltage is low)?
2) Can anyone collaborate the dedicated battery power wire? I do not see one when I inspect my battery area.
3) What exactly causes the transmission to physically engage in forward or reverse gear? I wonder if that component has failed.

Thanks

 

[NDT]

1. Yes on the WTEC II the shift selector and the trans ECU are the same box. If volts were low, you would get a code for that.
2. No such dedicated wire
3. Numerous solenoids in the transmission open valves which directs hydraulic pressure to clutches. Nothing wrong with them.

Now PLEASE go ohm out the sensor that the ECU is telling you is not reading right. If you need help with ohming out something, let us know. The diagnostic book shows you how.

 

[D-Fields]

I have visually inspected the wires and harness. Nothing looks stressed or warn. The sensors look unscathed and in good condition. I have not gotten to ohm'ing out all of the wires as suggested.

Two new ideas have arisen:
1) Once the engine is started, the transmission will not attempt to go into gear. Would the speed sensors really be relevant since the speed is at 0? If I rev the engine, while in gear, after a bit, I do get the 25 error. This makes me think that the sensors work as it is true the engine is spinning but nothing is coming out of the transmission.
2) A local mechanic, who is good with Cat's but admitted he knows little about Alison's mentioned the one thing he has seen is that the ECU(??) has a dedicated power lead from the batteries and if its not perfect problems happen. This struck a chord because prior to the problem I was monkeying with the batters to charge the older ones.

Here are my current questions.
1) Does the shift selector get its power from the ECU? Given that it lights up, does this mean that the ECU is getting power (perhaps voltage is low)?
2) Can anyone collaborate the dedicated battery power wire? I do not see one when I inspect my battery area.
3) What exactly causes the transmission to physically engage in forward or reverse gear? I wonder if that component has failed.

Thanks

What type of ECU do you have?
If it's the TCM-2100 from Powertrain Control Solutions, there is a way to diagnost the transmission via the flashing lamp close to the shift lever.
The manual explains in detail the proccess.

 

[Skyhawk13205]

I have visually inspected the wires and harness. Nothing looks stressed or warn. The sensors look unscathed and in good condition. I have not gotten to ohm'ing out all of the wires as suggested.

Two new ideas have arisen:
1) Once the engine is started, the transmission will not attempt to go into gear. Would the speed sensors really be relevant since the speed is at 0? If I rev the engine, while in gear, after a bit, I do get the 25 error. This makes me think that the sensors work as it is true the engine is spinning but nothing is coming out of the transmission.
2) A local mechanic, who is good with Cat's but admitted he knows little about Alison's mentioned the one thing he has seen is that the ECU(??) has a dedicated power lead from the batteries and if its not perfect problems happen. This struck a chord because prior to the problem I was monkeying with the batters to charge the older ones.

Here are my current questions.
1) Does the shift selector get its power from the ECU? Given that it lights up, does this mean that the ECU is getting power (perhaps voltage is low)?
2) Can anyone collaborate the dedicated battery power wire? I do not see one when I inspect my battery area.
3) What exactly causes the transmission to physically engage in forward or reverse gear? I wonder if that component has failed.

Thanks

remarks
1. The output speed sensor is an tonal type that counts the rotations. If the sensor resistance is out of range it will generate a fault during the ECU BITE on startup.
2. The ECU under voltage and constant power ups and power downs can cause corruption of data, intermittent unrelated faults and damage to ECU, but it is unlikely.

Questions
1. The keypad is the ECU and the relays to power up your ECU are in the VIM behind the passenger kick panel. If your keypad is lighted up and produce if error codes most likely you have good power.
2. The transmission shifting is electronic controlled, hydraulic actuated clutch packs. The tranmission oil pump generates hydraulic pressure, then the ECU commands a shift the ECU uses PWM signal to open a solenoid valve in the valve body to open porting pressure to the specific clutch pack. Usually if a failure in a solenoid the ECU will generate a hi/low/open solenoid fault. A low pressure /no pressure or slipping clutch will produce a ratio fault.

 

[Reworked LMTV]

The output speed sensors are so notorious, I keep a spare onboard.