stangman1976

The Heated Oxygen Sensor (HO2S) is monitored for switching. The test fails when the HO2S does not switch due to circuit or fuel at or exceeding a calibrated limit

Possible Causes
Electrical:
# Short to VPWR in the harness or HO2S.
# Water in the harness connector.
# Open/shorted HO2S circuit.
# Corrosion or poor mating terminals and wiring.
# Damaged HO2S.
# Damaged PCM.
Fuel System:
# Excessive fuel pressure.
# Leaking/contaminated fuel injectors.
# Leaking fuel pressure regulator.
# Low fuel pressure or running out of fuel.
# Vapor recovery system.
Induction System:
# Air leaks after the MAF.
# Vacuum Leaks.
# PCV system.
# Improperly seated engine oil dipstick.
EGR System:
# Leaking gasket.
# Stuck EGR valve.
# Leaking diaphragm or EVR.
Base Engine:
# Oil overfill.
# Cam Timing.
# Cylinder compression.
# Exhaust leaks before or near the HO2S(s).