PACCAR MX (2004 Emissions) Fault Code: P0278 Cylinder 6 – Torque Contribution Too Low

PACCAR MX (2004 Emissions) Fault Code: P0278 Cylinder 6 – Torque Contribution Too Low

SET CONDITIONS:
The PCI ECU (D420) detects that the combustion contribution of cylinder 6 is lower 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:
1. Faulty cylinder 6 injector (under-fueling)
2. Faulty MX Engine Brake cylinder 6
3. Symptom: Slightly reduced power:
– Incorrect valve clearance
– Major imbalance in the drive shaft
4. Symptom: Engine block vibration at high load, damaged flywheel
5. Mechanical defect (for example damaged cam follower or broken valve)

ADDITIONAL INFORMATION:
1. The PCI ECU can detect and identify the cylinder contribution of every cylinder based on analysis of the rotational speed of the crankshaft using a:
– Cylinder-to-cylinder engine speed comparison and
– Cylinder-to-cylinder rotational crankshaft acceleration comparison

2. This DTC can be the result of another DTC that indicates too high of a combustion contribution of another cylinder.