Have just had a problem with a 2004 Beaver Marquis Allison 4000 6 speed trans at 42000 mi.
When coming to corner of highway and using engine brake noticed that engine brake did not engage. After stopping "check transmission" light came on and transmission stayed in 5th gear. When arriving at destination as few miles later shut Coach off and then restarted, all was OK.
On return to home same problem appeared 4 more times, did not use engine brake, so thinking that when down shifting to stop this occurred.
Does anyone know what solving this problem involves.
Transmission is at fullmark for the Transynd fluid.
One other symptom is that when initially engaging transmission to move forward there is a seemingly longer delay than usual for trans to engage and it comes into gear hard. In reverse there is no delay.