The oxygen sensors supply the computer with a signal that indicates a rich or lean condition during engine operation. This input information assists the computer in determining the proper air/fuel ratio. A low voltage signal from one or more sensors indicates too much oxygen in the exhaust (lean condition) and, conversely, a high voltage signal indicates too little oxygen in the exhaust (rich condition). The oxygen sensors are threaded into the exhaust manifold and/or exhaust pipes on all vehicles. Heated oxygen sensors are used on all models to allow the engine to reach the closed loop faster. A faulty oxygen sensor due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit can cause the following symptoms.
Do not pierce the wires when testing heated oxygen sensors, as this can lead to wiring harness damage. Backprobe the connector to properly read the voltage of HO2S.When testing the oxygen sensor voltage signal, it should correspond to the values shown in this chart
NOTE: If excessive force is needed to remove the sensors, lubricate them with penetrating oil prior to removal.