Download Service Manual - SRC Power Systems

DTC P0172 Fuel Trim Low
Conditions for Setting the DTC
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Heated Oxygen Sensor
Check Condition-Engine running
Fault Condition-BLM (Block Learn Memory) less than 50% for 2 seconds.
MIL-On
Circuit Description
The EGO (Exhaust Gas Oxygen) sensor is used to determine if the fuel flow to the engine is correct
by measuring the oxygen content in the exhaust gas. The ECM uses this information to correct the fuel
flow with the BLM (Block Learn Memory). This fault will set if the BLM exceeds -50% fuel corrections.
Diagnostic Aid
SPN 65565
FMI 1
Fuel System High secondary fuel pressure will cause the system to run rich. A faulty fuel Mixer or
pressure regulator may also cause the system to run rich.
FCV A faulty fuel control valve can cause the system to run rich.
Fuel Quality A drastic variation in fuel quality (very high butane content) may cause the fuel system to
run rich.
Air Filter A plugged, damaged or modified air filter may cause the system to run rich.
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