Oxygen Sensor: Testing and Inspection

HEATED OXYGEN SENSOR CHECK

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

- MB991316: Test Harness
- MB991658: Test Harness

Heated oxygen sensor (front) [Except for California]

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 [4.5 - 8.0 ohms at 20 °C (68 °F)] between terminal No. 1 and terminal No. 2 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. Rev the engine for 5 minutes or more with the engine speed of 2,500 r/min.
6. Connect a digital voltage meter between terminal No. 3 and terminal No. 4.
7. 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 8 V is applied to the heated oxygen sensor heater.

NOTE: If the temperature of sensing area does not reach the high temperature [of approximately 400 °C (752 °F) or more] even though the heated oxygen sensor is normal, the output voltage would be possibly low in spite of the rich air/fuel ratio. Therefore, if the output voltage is low, use a jumper wire to connect terminal No. 1 and terminal No. 2 of the heated oxygen sensor with a (+) terminal and (-) terminal of 8 V power supply respectively, then check again.

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

Heated oxygen sensor (front) [California]

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 [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. Rev the engine for 5 minutes or more with the engine speed of 2,500 r/min.
6. Connect a digital voltage meter between terminal No. 2 (black clip) and terminal No. 4 (white clip).
7. 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 8 V is applied to the heated oxygen sensor heater.

NOTE: If the temperature of sensing area does not reach the high temperature [of approximately 400 °C (752 °F) or more] even though the heated oxygen sensor is normal, the output voltage would be possibly low in spite of the rich air/fuel ratio. Therefore, if the output voltage is low, use a jumper wire to connect terminal No. 1 (red clip of special tool) and terminal No. 3 (blue clip of special tool) of the heated oxygen sensor with a (+) terminal and (-) terminal of 8 V power supply respectively, then check again.

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

Heated oxygen sensor (rear) [Except for California]

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 [4.5 - 8.0 ohms at 20 °C (68 °F)] between terminal No. 1 and terminal No. 2 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. Drive at 50 km/h (31 mph) or more for 10 minutes.

6. Connect a digital voltage meter between terminal No. 3 and terminal No. 4.
7. Measure the output voltage of the heated oxygen sensor under the following driving.
- Transaxle: 2nd speed (CVT: "L" range)
- Drive with wide open throttle
- Engine: 3,500 r/min or more

NOTE:
- If the temperature of sensing area does not reach the high temperature [of approximately 400 °C (752 °F) or more] even though the heated oxygen sensor is normal, the output voltage would be possibly low in spite of the rich air-fuel ratio.
- When the vehicle is driven with high loads, the temperature of the sensing area of the heated oxygen sensor is sufficiently high. Thus, it is not necessary to apply the voltage to the heater.

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

Heated oxygen sensor (rear) [California]

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 [4.5 - 8.0 ohms at 20 °C (68 °F)] between terminal No. 1 and terminal No. 2 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. Drive at 50 km/h (31 mph) or more for 10 minutes.

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. 1 and terminal No. 2 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. Drive at 50 km/h (31 mph) or more for 10 minutes.