PACCAR MX (2004 Emissions) Fault Code: U177D Accelerator Pedal Sensor 1 Duty Cycle – Data Valid but Too High on ECU (D420) Pin (B41)

PACCAR MX (2004 Emissions) Fault Code: U177D Accelerator Pedal Sensor 1 Duty Cycle – Data Valid but Too High on ECU (D420) Pin (B41)

SET CONDITIONS:
The PCI ECU (D420) detects that the duty cycle of accelerator pedal position sensor 1 is higher than expected.

DIAGNOSTIC CONDITION:
This diagnostic runs continuously when the ignition is on.

CORRESPONDING OBD READINESS MONITOR:
None

RESET CONDITION:
This DTC changes to inactive when the fault is no longer detected. To validate the repair, monitor the accelerator pedal sensors with the diagnostic service tool.

REPAIR VERIFICATION:
1. Clear all DTCs.
2. Test drive or operate the vehicle to meet the diagnostic conditions and set conditions.
3. Did the DTC come back?
– No, repair successful
– Yes, repair unsuccessful

POSSIBLE CAUSES:
Faulty accelerator pedal or wiring

ADDITIONAL INFORMATION:
The accelerator pedal position is determined by two sensors (1 and 2) inside the accelerator pedal. The sensor outputs are PWM signals at a fixed frequency of 180 to 220 Hz. Sensor signals 1 and 2 are reversed compared to each other, meaning that by pressing the accelerator more, sensor 1 shows a decreasing PWM signal and sensor 2 shows an increasing PWM signal. The PCI ECU monitors both sensors separately and together.