Accelerator pedal sensor, PWM signal low
Reset the control unit using SDP3 or Allison diagnostic tool and check whether the control unit locks onto a correct source.Check the cable harness from the accelerator pedal sensor to control unit pins 12, 44 and 58.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: P1891.PWM means Pulse-Width Modulation.The control unit has found a PWM type accelerator pedal sensor.The fault code is set when the control unit has detected that the PWM signal from the accelerator position sensor has been at less than 4.9% for 5 seconds.The control unit uses a preselected accelerator pedal position value.The fault code is cleared automatically, when the vehicle has completed 40 start-up cycles without the fault being detected again.
Diagnostic depth
The control unit has detected that the PWM signal from the accelerator pedal sensor has been less than 4.9%.
Incorrect source for accelerator pedal position information may be selected by control unit. Damage to the cable harness can also generate this fault code.