Oxygen Sensor System

EXCEPT MODEL 300 SL

1. Warm the engine up to normal operating temperature.
2. With the engine off, disconnect the oxygen sensor and ground the single wire connector going to the ECU. This will induce a full rich condition. The oxygen sensor wires are located under the carpet on the passenger side of the tunnel.

Fig. 37 Oxygen Sensor Connection Location:

3. Connect a volt meter to the single wire coming from the oxygen sensor and start the engine.
4. Watch the voltage reading. The oxygen sensor output should be 0.45 - 1.0 vdc.

a. If the reading is 0.45 - 1.0 v. oxygen sensor is functioning properly.
b. If the reading is lower than 0.45 v., replace the oxygen sensor.

Oxygen Sensor Heater Circuit


5. Disconnect the oxygen sensor heater wires at the two terminal connector.

6. Using a set of suitable jumper leads connect an amperage meter to the heater wires. The meter should display a 0.5 - 1.3 amp. draw. If amperage is incorrect oxygen sensor heating element is faulty, and the oxygen sensor should be replaced. If an ammeter is not available, check the heater resistance with an ohmmeter. Readings should be 3 ohms (cold) or 13 ohms (hot). If either test results are not as specified, replace the oxygen sensor.

Fig. 96 O2 Sensor Connection Location:

MODEL 300 SL

1. Warm the engine up to normal operating temperature.
2. With the engine off, disconnect the oxygen sensor connector at the transmission tunnel. Ground the terminal corresponding to the oxygen sensor signal leading to the ECU on the tunnel. This will induce a full rich condition.

Fig. 97 Terminal Location:

3. Connect a volt meter to the oxygen sensor signal terminal coming from the sensor.
4. Start the engine and watch the voltage reading.

a. If the reading is 0.45 - 1.0 v. oxygen sensor is functioning properly.
b. If the reading is lower than 0.45 v., replace the oxygen sensor.