PACCAR MX (2004 Emissions) Fault Code: P171C EGR Flow Response – Increase Too Slow

PACCAR MX (2004 Emissions) Fault Code: P171C EGR Flow Response – Increase Too Slow

SET CONDITIONS:
The PCI ECU (D420) detects that the EGR mass flow increase is too slow during changes in the commanded EGR mass flow from a low to high rate.

DIAGNOSTIC CONDITION:
This diagnostic runs:
1. When the engine speed is between 1000 and 1450 rpm and
2. The engine mode is DPF regeneration or SCR heating or SCR high efficiency or standard

CORRESPONDING OBD READINESS MONITOR:
EGR 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. Leaking EGR system
2. Clogged EGR system
3. Clogged EGR pressure difference sensor venturi
4. Sticking EGR valve

ADDITIONAL INFORMATION:
1. The engine NOx emission is, among others, controlled by varying the EGR flow toward the inlet manifold of the engine.

2. For this diagnostic, the EGR pressure difference sensor (F751) is used to measure the EGR mass flow during changes in the commanded EGR mass flow from a lower to higher flow rate.