Oxygen Sensor: Testing and Inspection

HEATED OXYGEN SENSOR CHECK

Required Special Tools:
- MB991958: Scan tool (MUT-III Sub Assembly)
- MB991824: V.C.I
- MB991827: USB Cable
- MB991910: Main Harness A

- MB991316: Test Harness
- MD998464: Test Harness








1. Using scan tool MB991958, observe HO2S reading If values are unsatisfactory, or if a scan tool is not available, use the following procedure:
1. Disconnect the heated oxygen sensor connector and connect special tool MD998464 to the connector on the heated oxygen sensor side
2. Make sure that there is continuity [4.5-8.0 Ohms at 20 °C (68 °F)] between terminal No. 1 (red clip) and terminal No. 3 (blue clip) on the heated oxygen sensor connector.
3. If there is no continuity, replace the heated oxygen sensor
4. Warm up the engine until engine coolant is 80 °C (176 °F) or higher.
5. Perform a tracing for 5 minutes or more with the engine speed of 4,500 r/min.
6. Connect a digital voltage meter between terminal No. 2 (black clip) and terminal No. 4 (white clip).




2. While repeatedly revving the engine, measure the heated oxygen sensor output voltage.

CAUTION:
- Be very careful when connecting the jumper wire; incorrect connection can damage the oxygen sensor.
- Be careful the heater is broken when voltage of beyond 8 V is applied to the oxygen sensor heater.

NOTE: If the sufficiently high temperature (of approximate 400 °C or more) is not reached although the oxygen sensor is normal, the output voltage would be possibly low although the rich air-fuel ratio Therefore, if the output voltage is low, use a jumper wire to connect the terminal No. 1 (red clip of special tool) and the terminal No. 3 (blue clip of special tool) of the oxygen sensor with a (+) terminal and (-) terminal of 8 V power supply respectively, then check again.

3. If the output voltage is not within the standard value, replace the heated oxygen sensor.

NOTE: For removal and installation of the heated oxygen sensor, refer to Exhaust Pipe and Main Muffler.








1. Using scan tool MB991958, observe HO2S reading. If values are unsatisfactory, or if Scan tool is not available, use the following procedure:
1. Disconnect the heated oxygen sensor connector and connect special tool MB991316 to the connector on the heated oxygen sensor side.
2. Make sure that there is continuity [11-18 Ohms at 20 °C (68 °F)] between terminal No. 1 (red clip) and terminal No. 3 (blue clip) on the heated oxygen sensor connector.
3. If there is no continuity, replace the heated oxygen sensor.
4. Warm up the engine until engine coolant is 80 °C (176 °F) or higher.
5. Perform a tracing for 5 minutes or more with the engine speed of 4,500 r/min.
6. Connect a digital voltage meter between terminal No. 2 (black clip) and terminal No. 4 (white clip).




2. While repeatedly revving the engine, measure the heated oxygen sensor output voltage.

CAUTION:
- Be very careful when connecting the jumper wire; incorrect connection can damage the oxygen sensor.
- Be careful the heater is broken when voltage of beyond 8 V is applied to the oxygen sensor heater.

3. If the output voltage is not within the standard value, replace the heated oxygen sensor.

NOTE: If the sufficiently high temperature (of approximate 400 °C or more) is not reached although the oxygen sensor is normal, the output voltage would be possibly low although the rich air-fuel ratio .Therefore, if the output voltage is low, use a jumper wire to connect the terminal No. 2 and the terminal No. 1 of the oxygen sensor with a (+) terminal and (-) terminal of 12 V power supply respectively, then check again.

NOTE: For removal and installation of the heated oxygen sensor, refer to Exhaust Pipe and Main Muffler.