PACCAR MX (2004 Emissions) Fault Code: P1490 EGR Gas Flow Detected – While the EGR Valve is Closed

PACCAR MX (2004 Emissions) Fault Code: P1490 EGR Gas Flow Detected – While the EGR Valve is Closed

SET CONDITIONS:
The PCI ECU (D420) detects that a certain level of EGR gas mass flow is present, measured by the EGR pressure difference sensor (F751), while the EGR valve is commanded closed.

DIAGNOSTIC CONDITION:
This diagnostic runs when the engine is running.

CORRESPONDING OBD READINESS MONITOR:
None

RESET CONDITION:
This DTC changes to INACTIVE when the ignition is keyed OFF and ON again and the diagnostic runs and passes.

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:
1. PCI software bug
2. Freezing of the EGR venturi pressure ports
3. Freezing of the EGR pressure difference sensor pressure ports
4. Contamination of the EGR venturi pressure ports
5. Deviation of the EGR pressure difference sensor (F751)
6. Contamination of the EGR valve due to soot (only applicable if EGR valve position control DTCs are also present)
7. Failure of the EGR valve mechanism (only applicable if EGR valve position control DTCs are also present)

ADDITIONAL INFORMATION:
1. One way in which the engine NOx emission is controlled is by varying the EGR gas mass flow toward the inlet manifold of the engine.
2. The EGR gas mass flow is calculated using the EGR pressure difference sensor (F751) and the EGR temperature sensor (F749).
3. EGR gas mass flow toward the inlet manifold of the engine is controlled by the EGR valve module (L095) but is mainly dependent on the pressure before turbine.