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
- MB991911: Main Harness B
- MB991658: Test Harness Set
- MD998464: Test Harness



1. Using the 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 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 of special tool) and terminal No.3 (blue clip of special tool) 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 revving for 5 minutes or more with the engine speed of 4,500 r/min.
6. Connect a digital voltage meter between terminal No.1 and terminal No.2.




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 heated oxygen sensor.
- Be careful the heater is broken when voltage of beyond 12 volts is applied to the heated oxygen sensor heater.

NOTE: If the sufficiently high temperature [of approximate 400°C (752°F) or more] is not reached although the heated 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 jumper wires to connect the terminal No.3 and the terminal No.4 of the heated oxygen sensor with a (+) terminal and (-) terminal of 12 volts 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 Manifold.



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 MB991658 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.3 and terminal No.4 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 revving for 5 minutes or more with the engine speed of 4,500 r/min.
6. Connect a digital voltage meter between terminal No.4 and terminal No.2.




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 heated oxygen sensor.
- Be careful the heater is broken when voltage of beyond 12 volts is applied to the heated oxygen sensor heater.

NOTE: If the sufficiently high temperature [of approximate 400°C (752°F) or more] is not reached although the heated 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 jumper wires to connect the terminal No.3 and the terminal No.4 of the heated oxygen sensor with a (+) terminal and (-) terminal of 12 volts 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.