Oxygen Sensor Preliminary Tests

Check for the following conditions which can cause Oxygen Sensor Faults to set without requiring Oxygen Sensor replacement:

Common issues for lean faults:

• Vacuum leaks - check for failed or loose vacuum lines, leaking intake gaskets, or any other source of un-metered air leaks (leaks after the Mass Air Flow Sensor).
• Restricted fuel filter or bent/pinched fuel system lines.
• Incorrect input from other sensors, such as the Mass Air Flow Sensor, which may not always set a fault.
• Engine misfire.
• Exhaust leaks.
• Camshaft timing.

Common issues for rich faults: 

• Leaking or faulty fuel injector.
• Fuel injector driver shorted in ECM, or wiring short for injectors (short to ground).
• Leaking or faulty fuel pressure regulator or restricted return line.
• Faulty fuel pump or fuel pump driver module.
• Incorrect input from other sensors, such as the Mass Air Flow Sensor, which may not always set a fault.
• Aftermarket components or performance chips.
• Camshaft timing.