Gear changing prevention function
Check that there is no damage or short circuits in the external cable harness or any switch connected to pins 1, 3 and 42.If no fault is detected, contact an Allison dealer.
What you'll see
No driver-visible symptom recorded.
System reaction
The Allison fault code number is: P071D.The gear change prevention function is activated when pins 1 and 3 are connected together and pin 42 is connected to ground. The fault code can only be set if the control unit in the vehicle has been programmed for fire engines.The fault code is cleared automatically, when the vehicle has completed 40 start-up cycles without the fault being detected again.
Diagnostic depth
Input signals to the control unit for activation of the gear changing prevention function are incorrect.
The control unit has detected two different states on pins 1 and 42 in the control unit.