Engine torque limitation (SEM) not possible
Check the cable harness between the coolant temperature sensor and control unit pins 58 and 35. If no fault is found, contact an Allison dealer.
What you'll see
No driver-visible symptom recorded.
System reaction
The Allison fault code number is: P2637.This function is used for quicker gear changes and to achieve a more constant torque which reduces clutch temperature and extends clutch life.The fault code is set when the control unit detects that the engine has not responded to the request for torque reduction from the control unit.The torque limiter function is activated in the calibration.The fault code is cleared automatically, when the vehicle has completed 40 start-up cycles without the fault being detected again.
Diagnostic depth
The engine does not respond to the request for torque reduction from the control unit.
One cause of this fault code is that the engine does not allow the gearbox control unit to limit torque.