Forum Discussion

astro001's avatar
astro001
Explorer
Apr 02, 2017

Allison MD3000MH not engaging

Allison Transmission, LONG STORY!
In December 2015 while in Winchester, VA I stopped for diesel. After fueling I started the motorhome when I touched D on the shift pad it would not engage and the 6 was blinking. Tried R and the same blinking R. I shifted back to N and pushed the shift up arrow and shift down arrow at the same time twice (once checks oil level) and displayed transmission error code d12214. Quick google search showed Input Engine Speed Sensor. I revved the engine in N to 1500 RPM and let it return to idle. Transmission engaged normally. Since it had been nasty and rainy, when I got home I cleaned the sensor connector and added clear silicone. No problems since. Fast forward to Thursday, Leaving for Camp Blanding for the weekend. I warmed up the MH, pulled it out into the driveway. When I restarted to leave, same symptoms (Blinking 6) as above. Error code d12214. Revved engine, engaged fine. Drove to Camp Blanding, parked, restarted, same problem. Friday morning I called Allison tech support. This is a common problem and the Allison computer reads the engine RPM as too low. They referred me to North Florida Western Star on University Blvd. Called them with Allison Serial number, Part cost was $78.90. They had it pulled when I arrived. I also noticed the sell Allison Transynd for $42.00/gal. Took 5 minutes to install. Problem solved.
Class A

10 Replies

Sort By
  • 1SG's avatar
    1SG
    Explorer
    Apr 04, 2017
    Our companies garbage trucks all have Allison transmissions and yes the speed sensor is usually the problem when you have a no shift problem. Our sensors are located on the tranny's tailshaft housing. I was told a couple of times by Allison techs keep that sensor wire connection dry. Do not use anything on it including dielectic grease.

    Paul
  • Jim's avatar
    Jim
    Explorer
    Apr 03, 2017
    Great write up, thanks for letting us know!
  • tropical36's avatar
    tropical36
    Explorer
    Apr 03, 2017
    astro001 wrote:
    Yes, remove wire plug, remove 1/2" retainer bolt. I used pliers to pull out the old sensor. No fluid leaks out. Lube O ring on new sensor with ATF. It did take a little force to push the new sensor in. Replace retainer bolt and wire socket. Done. Takes 5 minutes.

    All this is good to know, so thanks for that info and will take a survey of this thingy, next time I'm down under the coach for a looksee.
  • cross21114's avatar
    cross21114
    Explorer
    Apr 03, 2017
    Man, you learn so much on this forum. Great job diagnosing and fixing the problem.
  • Teacher_s_Pet's avatar
    Teacher_s_Pet
    Explorer
    Apr 02, 2017
    Had the same problem 7-8 years ago, Freightliner had bound the wiring harness to tight to the frame, caused the plug to "wallow-out" and loose connection. Allison dealer in Ft Wayne IN replaced the plug and extended harness length, charged me $150 for 20 minutes work including the parts. We never bothered to file a claim with Freightliner, just happy to be back on the road in less than an hour.
  • astro001's avatar
    astro001
    Explorer
    Apr 02, 2017
    Yes, remove wire plug, remove 1/2" retainer bolt. I used pliers to pull out the old sensor. No fluid leaks out. Lube O ring on new sensor with ATF. It did take a little force to push the new sensor in. Replace retainer bolt and wire socket. Done. Takes 5 minutes.
  • tropical36's avatar
    tropical36
    Explorer
    Apr 02, 2017
    astro001 wrote:
    The sensor is located on the drivers side of the transmission close to the engine. I searched the part number on ebay and found the sensor for $40.00. Hopefully the below picture displays. The picture is of the old part.

    So, it just screws into the tranny body and plugs into some wiring? Looks like it also has an O ring, so assume it's in an oil cavity.
  • astro001's avatar
    astro001
    Explorer
    Apr 02, 2017
    The sensor is located on the drivers side of the transmission close to the engine. I searched the part number on ebay and found the sensor for $40.00. Hopefully the below picture displays. The picture is of the old part.
    Click For Full-Size Image.
  • tropical36's avatar
    tropical36
    Explorer
    Apr 02, 2017
    astro001 wrote:
    Allison Transmission, LONG STORY!
    In December 2015 while in Winchester, VA I stopped for diesel. After fueling I started the motorhome when I touched D on the shift pad it would not engage and the 6 was blinking. Tried R and the same blinking R. I shifted back to N and pushed the shift up arrow and shift down arrow at the same time twice (once checks oil level) and displayed transmission error code d12214. Quick google search showed Input Engine Speed Sensor. I revved the engine in N to 1500 RPM and let it return to idle. Transmission engaged normally. Since it had been nasty and rainy, when I got home I cleaned the sensor connector and added clear silicone. No problems since. Fast forward to Thursday, Leaving for Camp Blanding for the weekend. I warmed up the MH, pulled it out into the driveway. When I restarted to leave, same symptoms (Blinking 6) as above. Error code d12214. Revved engine, engaged fine. Drove to Camp Blanding, parked, restarted, same problem. Friday morning I called Allison tech support. This is a common problem and the Allison computer reads the engine RPM as too low. They referred me to North Florida Western Star on University Blvd. Called them with Allison Serial number, Part cost was $78.90. They had it pulled when I arrived. I also noticed the sell Allison Transynd for $42.00/gal. Took 5 minutes to install. Problem solved.

    Don't suppose it's worth it, for carrying a spare, but where is this sensor, on the Tranny, just in case, I ever need to take a looksee.

About Motorhome Group

38,718 PostsLatest Activity: May 03, 2025