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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.