Oxygen Sensor: Testing and Inspection

NOTE: A total of 4 oxygen sensors (left, right, pre-catalyst and post catalyst) are used when equipped with the Medium Duty Emission Cycle (MDC) engine package. Only 2 oxygen sensors (left and right) are used with the Heavy Duty Emission Cycle (HDC) engine.

Fig. 11 Pre-Catalyst/Post Catalyst Oxygen Sensors - MDC Engines:

The pre-catalyst O2S sensor is located on the inlet end of the catalytic converter. The post catalyst 025 sensor is located on the outlet end of the catalytic converter.

Fig. 65 Left/Right Oxygen Sensor Locations - HDC/MDC Engines:

The left and right sensors are located on the left and right exhaust downpipes.

Each O2S heating element can be tested with an ohmmeter as follows:

Disconnect the O2S sensor connector. Connect the ohmmeter test leads across the white wire terminals of the sensor connector. Resistance should be between 5 and 7 ohms. Replace the sensor if the ohmmeter displays an infinity (open) reading.