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
- MB991658: Test Harness

Heated oxygen sensor (front)





1. Disconnect the heated oxygen sensor connector and connect special tool MB991658 to the connector on the heated oxygen sensor side.
2. Measure the resistance between terminal No. 1 and terminal No. 2 on the heated oxygen sensor connector.
Standard value: 4.5 - 8.0ohms [at 20° C (68°F)]
3. If the resistance deviates from standard value, 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 2,000 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.
Standard value:

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 8V is applied to the 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 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 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.
NOTE:
For removal and installation of the heated oxygen sensor, refer to Exhaust Pipe and Main Muffler - Removal and installation Service and Repair.

Heated oxygen sensor (rear)





1. Disconnect the heated oxygen sensor connector and connect special tool MB991658 to the connector on the heated oxygen sensor side.
2. Measure the resistance between terminal No. 1 and terminal No. 2 on the heated oxygen sensor connector.
Standard value: 4.5 - 8.0ohms [at 20° C (68° F)]
3. If the resistance deviates from standard value, 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
- Drive with wide open throttle
- Engine: 3,500 r/min or more
Standard value:

NOTE:
If the temperature of sensing area does not reach the high temperature [of approximately 400°C (752°F) or more] even though the oxygen sensor is normal, the output voltage would be possibly low in spite of the rich air-fuel ratio.

NOTE:
When the vehicle is driven with high loads, the temperature of the sensing area of the 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.
NOTE:
For removal and installation of the heated oxygen sensor, refer to Exhaust Pipe and Main Muffler - Removal and installation Service and Repair.