ALLISON TRANS NOT SHIFTING TO 6th GEAR

[AARONDENISE]

WE ARE HAVING TROUBLE GETTING OUT ALLISON TRANSMISSION TO SHIFT TO 6th GEAR..It would start going slower no matter how hard we pushed on gas so WE COULD LET OFF THE GAS A LITTLE AND IT WOULD AUTOMATICALLY SHIFT ITSELF..NOW IT WONT DO THAT..WE HAVE TO PUSH NEUTRAL & THEN PUSH 6th GEAR AND ITS STARTING TO DO THAT IN 5th GEAR OCCASSIONALLY ALSO. ANYONE HAVE ANY SUGGESTIONS? WE ARE NOT GETTING ANY ERROR CODES ON PUSHBUTTON. ANY HELP WOULD BE APPRECIATED

[Mike Canter]

When is the last time you changed both fuel filters. If they are blocked and the motor is not getting enough fuel then it will be down on power. It has to get to 55-57 mph to shift into 6th gear.

[AARONDENISE]

WE WILL CHECK THAT OUT & SEE..WE WERE GOING 65 OR SO WHEN IT WOULDN'T SHIFT TO 6th

[hzjcm8]

Quote:

Originally Posted by AARONDENISE WE WILL CHECK THAT OUT & SEE..WE WERE GOING 65 OR SO WHEN IT WOULDN'T SHIFT TO 6th

AARONDENISE,

Shift points are programmed into the TCM based on input speed, output speed and throttle setting. So, if you're not going into gear, I'd have the speed sensors and throttle position sensors checked.

[AARONDENISE]

Where is the throttle positioning sensor located? We were wondering if it was something to do with that. We have found a lot of things not connected or loosened up lately.

[Mike Canter]

Surely if a speed sensor or a throttle position sensor was bad you would get either a transmission fault code or an engine fault code and the appropriate warning light on the dash that it has been set. Since the OP has not metioned a problem in the other lower gears then I would say there is not a fault with either of those sensors and that is why I suggest that it is external to the motor and transmission and is caused by a reduction in power because one or both or the fuel filters are blocked either from Black Slime or because they haven't been changed in over 10,000 miles.

[Skip426]

Quote:

Originally Posted by AARONDENISE Where is the throttle positioning sensor located? We were wondering if it was something to do with that. We have found a lot of things not connected or loosened up lately.

The TPS, is attached to the throttle pedal, and supplies a voltage signal to the engine / trans control modules. If , as Mike has stated, you have pluged fuel ,or air filters, then the throttle possision does not corolate with the engine RPM required for the up-shift, the trans controler will hold the trans in 5th gear. You should how-ever be able to force an up-shift, to 6th at any speed above 60mph by fully releasing the throttle, on level road, then easing back on the throttle to hold 6th after the shift. If an up-shift won't happen after releasing the throttle, and the coach holds 5th and slows down, a complete check of the trans operation is in order.