PACCAR MX (2004 Emissions) Fault Code: P128E Common Rail Fuel Pressure Control – Incorrect

PACCAR MX (2004 Emissions) Fault Code: P128E Common Rail Fuel Pressure Control – Incorrect

SET CONDITIONS:
The PCI ECU (D420) detects that the measured rail pressure is more than 1000 bar higher than the commanded rail pressure for more than 5 seconds.

DIAGNOSTIC CONDITION:
This diagnostic runs when the rail pressure operating state is: Rail discharge.

RESET CONDITION:
This DTC changes to inactive when the fault is no longer detected.

POSSIBLE CAUSES:
1. Blocked common rail pressure release valve return pipe
2. Malfunction on common rail pressure release valve

ADDITIONAL INFORMATION:
1. The rail pressure is closed-loop controlled. A comparison is made between the rail pressure commanded by the ECU and the rail pressure feedback measured by the common rail pressure sensor.

2. The common rail pressure release valve (L094) is used to decrease the rail pressure rapidly (dumping) during normal operation.
3. The rail pressure is measured in the common rail by the common rail pressure sensor (F854).