PACCAR MX (2004 Emissions) Fault Code: P1709 Lambda – Data Valid but Too Low During Overrun

PACCAR MX (2004 Emissions) Fault Code: P1709 Lambda – Data Valid but Too Low During Overrun

SET CONDITIONS:
The PCI ECU (D420) detects that the measured oxygen concentration in the exhaust is too low while coasting (fuel injection cut off) for more than 21 seconds.

DIAGNOSTIC CONDITION:
This diagnostic runs:
1. During coasting (no fuel injection) and
2. When the coolant temperature is above 50°C [122°F] and
3. The lambda sensor (F834) is in the operating mode (if applicable)

CORRESPONDING OBD READINESS MONITOR:
Exhaust gas sensors 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. Lambda sensor deviation (if equipped with lambda sensor)
2. NOx sensor before catalyst deviation (only if NOT equipped with lambda sensor)

ADDITIONAL INFORMATION:
IMPORTANT: Depending on the production date of the vehicle, either the lambda sensor (F834) or the NOx sensor before catalyst (F844) is used to determine the oxygen concentration in the exhaust gas.

1. Typically, low air/fuel ratio indicates low oxygen concentration in the exhaust system.
2. When no combustion takes place, the oxygen concentration must be almost equal to the ambient air concentration (approximately 20%) after some time.