Checking Oxygen Sensor

Oxygen sensor function is also checked by measuring the duty cycle, as described in the tests above. To properly evaluate the oxygen sensor, the rest of the oxygen sensor system must first be tested in the sequence described above.

Start the engine and let it run until it reaches normal operating temperature. If the engine is already warm, run it for at least two minutes. With the engine running, remove the crank-case ventilation hose from its connection at the intake manifold, as shown in Fig. 5-1. When the open port on the intake manifold is plugged, the duty cycle reading should drop. If it does not respond, the oxygen sensor is faulty and should be replaced.

Fig. 5-1.

Crankcase ventilation hose A removed for duty cycle measurement. Intake manifold connection B should be plugged for test.