2001 Marquis Amethyst trans locks in first gear

[Mike Sulley]

Hi all,  newbie here.  We are stilllp
P learning about our new coach.  We recently purchased a 2001 Marquis Amethyst with a 505 hp Cat C12 and a HD 4000 RV transmission.  It recently started sifting into 1st gear when drive is selected, and refusing to up shift to 2nd.  Once in first, it won’t return to neutral or reverse.  We have to shift to neutral( it doesn’ t shift) and shut down the engine off.  On restarting it will return to neutral and can be shifted to reverse( which works).  Upon shifting to drive, it locks up all over again.

Our Mechanic has down loaded the transmission error codes, and saw a “transmission speed sensor” code, and
possibly an ABS code.  Does my coach even have ABS ?  He saw no other codes.

We have ordered a new speed sensor for the transmission.  Has anyone else experienced this?  Does it sound legitimate?

Would appreciate any helpful insight anyone can offer.

Thanks so much.

Mike Sulley

[Eric Maclean]

Mike
The Allison 300/400 troubleshooting manual is loaded on the coach assist library .
It will show you how to get the fault codes by using the shift pad.
From there you can move to that particular fault code and troubleshoot the problem .
I can understand no up shift without the speed sensor but I don't understand it locking up.

First start by retrieving all the fault codes and go from there.

Eric

[Steve Huber Co-Admin]

Mike,
We had a somewhat similar issue with the 4000 transmission in our 2000 Marquis. It refused to shift out of 3rd and the codes didn't ID anything related. After the tech started moving the electrical harness going to the tranny, it started working. He diagnosed bad connections which he said were not an uncommon problem. We replaced the wire harness and no more problems.
Steve

[Mike Sulley]

Gentlemen thank you for your replies.  I used poor terminology when describing my problem as “ locking up”.  The transmission would not up-shift out of 1st gear.  When the mechanic initially scanned the “ speed sensor” codes, he thought they were old inactive codes as I had had this issue twice before.  Once miles from home.  Fortunately, the problem occurred when leaving his shop rather than out on the open road, and I was able to make it back to his shop.  We were leaving the shop after correcting some other issues.

Upon returning to his shop, he rescanned the codes and replaced the speed sensor.  Now all is well.  She drives nice again.

One quick follow up question.  When checking the transmission fluid level.  I know the trans should be at temp, but should the engine be idling in neutral like an auto trans in a car or with the engine off?  The dip stick doesn’t specify.

Thanks again for your quick replies.
Mike

[Eric Maclean]

Mike
The best and most accurate way to check the transmission fluid is by using the shift pad .
The dip sticks are not always accurate
The procedure is out lines in the Allison troubleshooting manual.

Either way the engine should be at idle in neutral at operating temperature which means you have to drive it for at least half an hour the transmission oil temp must reach at least 140 degrees before the TCM will allow a reading.
With the vehicle on a level surface , idling , in neutral,at operating temperature, two minutes of sitting still.
Then push the up and down arrows on the shift pad at the same time and observe the shift pad display.
It will start with OL ( for oil level ) and will then flash OK if at property level  or LO followed by the number of quarts or HI followed by the number of quarts .
It may a
So flash one of several codes to tell you you have not meet criteria for checking the fluid (. IE not warm enough )
Read the section in the troubleshooting manual or owners manual and follow the procedure it quick and easy once you learn how

Hope this helps
Eric.