Quick-Checking Oxygen Sensor System

Checking the duty cycle for fluctuation gives a quick indication that the system is functioning as intended. To check, the engine should be fully warmed up. Attach a duty cycle meter or dwell meter as described above, then start the engine and let it run for at least two minutes to warm the oxygen sensor. Remove the crankcase ventilation hose from the intake manifold as shown in Fig. 5-1 and plug the manifold connection. The duty cycle reading should drop and then fluctuate within a range of 25-65% (23-59° on a dwell meter). If the reading does not fluctuate, rev the engine several times. The reading should then fluctuate. Stop the engine and reconnect the hose. If the reading is incorrect, test the system in the sequence which follows.

Fig. 5-1.

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