OXYGEN SENSOR CHECK



OXYGEN SENSOR (FRONT)



1.Disconnect the oxygen sensor connector and connect the special tool test harness (MB991658) to the connector on the oxygen sensor side.


2.Measure the resistance between terminal No. 1 and No. 2 of the oxygen sensor connector.
Standard value: 4.5 - 8.0 Ω (at 20°C)
3.If the resistance deviates from the standard value, replace the oxygen sensor.
4.Warm up the engine until the engine coolant temperature is 80°C or higher.
5.Perform a racing for 5 minutes or more with the engine speed of 2,000 r/min.
6.Connect the digital voltmeter between terminal No. 3 and No. 4.
7.While repeatedly racing the engine, measure the oxygen sensor output voltage.
Standard value:
Engine
Oxygen sensor output voltage
Remarks
When racing the engine
0.6 - 1.0 V
If you make the air-fuel ratio rich by racing the engine repeatedly, a normal oxygen sensor will output a voltage of 0.6 - 1.0 V.
caution
  • Be very careful when connecting the jumper wire; incorrect connection can damage the oxygen sensor.
  • Exercise sufficient care so as not to apply voltage exceeding 8 V onto the oxygen sensor heater; otherwise the heater may be damaged.
note If the temperature of sensing area does not reach the high temperature (of approximately 400°C 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 the terminal No. 1 and No. 2 of the oxygen sensor with the (+) and (-) terminals of 8 V power supply respectively, then check the voltage again.
8.If the voltage deviates from the standard value, replace the oxygen sensor.
note For removal and installation of the oxygen sensor, refer to GROUP 15 - Exhaust Pipe, Main Muffler and Catalytic Converter .

OXYGEN SENSOR (REAR)


caution Drive test must be performed, while two persons are onboard, in a place where a full-throttle accelerating drive can be attempted safely.

1.Disconnect the oxygen sensor connector and connect the special tool test harness (MB991658) to the connector on the oxygen sensor side.


2.Measure the resistance between terminal No. 1 and No. 2 of the oxygen sensor connector.
Standard value: 4.5 - 8.0 Ω (at 20°C)
3.If the resistance deviates from the standard value, replace the oxygen sensor.
4.Warm up the engine until the engine coolant temperature is 80°C or higher.
5.Drive at 50 km/h or more for 10 minutes.
6.Connect the digital voltmeter between terminal No. 3 and No. 4.
7.Measure the output voltage of the oxygen sensor under the following driving.

  • Transmission: 2nd
  • Drive with wide open throttle
  • Engine: 3,500 r/min or more
Standard value:
Oxygen sensor output voltage
Remarks
0.6 - 1.0 V
High load operation makes air/fuel ratio richer and normal oxygen sensor also can output voltage of 0.6 - 1.0 V
note If the temperature of sensing area does not reach the high temperature (of approximately 400°C 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 voltage deviates from the standard value, replace the oxygen sensor.
note For removal and installation of the oxygen sensor, refer to GROUP 15 - Exhaust Pipe, Main Muffler and Catalytic Converter .