PACCAR MX (2004 Emissions) Fault Code: P1278 Cylinder 6 – Torque Contribution Too High

PACCAR MX (2004 Emissions) Fault Code: P1278 Cylinder 6 – Torque Contribution Too High

SET CONDITIONS:
The PCI ECU (D420) detects that the combustion contribution of cylinder 6 is higher relative to the other cylinders.

DIAGNOSTIC CONDITION:
This diagnostic runs when the engine is running at a steady speed and load, and the vehicle speed is steady.

CORRESPONDING OBD READINESS MONITOR:
Fuel system monitor

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

REPAIR VERIFICATION:
1. Clear all DTCs.
2. Test drive or operate the vehicle to meet the following conditions:
– Corresponding readiness monitor displays ‘Ready’
– Diagnostic conditions are met
– Set conditions are met
3. Did the DTC come back? (Can be pending, inactive or active)
– No, repair successful
– Yes, repair unsuccessful

POSSIBLE CAUSES:
Fault cylinder 6 injector (overfueling)

ADDITIONAL INFORMATION:
The PCI ECU is able to detect and identify several modes of combustion failure based upon analysis of the rotational speed of the engine. The results from the cylinder-to-cylinder engine speed and the measured combustion-induced rotational acceleration are compared against a stored value which is regularly updated when no faults are present. In this way, the cylinder contribution for each cylinder can be determined.