P1151 OBD Trouble Code

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Technical Description

Lack of HO2S-21 Switch, Sensor Indicates Lean

What does that mean?

A Heated Exhaust Oxygen (HO2S) sensor indicating lean at the end of a test is trying to correct for an over-rich condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time.

Symptoms

You will likely not notice any drivability problems.

Causes

A code P1151 may mean that one or more of the following has happened:

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)

Possible Solutions

• See the above list of causes and go from there.

Sources: MotorCraftService.com

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