Engine torque limitation (LRTP) not possible
Check the cable harness between the gearbox and control unit, particularly the electrical cable to pin 71 on the control unit. 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: P2641.The torque limiter request from the control unit is shut off.This function is used to protect the gearbox when driving slowly and when engine torque exceeds a predefined value.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.