Oxygen Sensor: Testing and Inspection

Oxygen Sensor Location:

Verify: That the engine is at normal operating temperatures.
The idle speed, timing, and CO content are correct.
The exhaust system between the catalytic converter and the cylinder head is not leaking.
The intake system is free from vacuum leaks.
The voltage supply and ground for the oxygen sensor heater is OK!
The coolant temperature sensor and oxygen sensor are connected.
That all electrical consumers are switched "OFF" and the radiator cooling fan is not running during the test.

1. Remove the cap from the CO test port.
2. Connect a suitable exhaust gas analyzer to the test port.
3. With the engine idling, check and record the CO level.
4. Remove the oil filler cap from the valve cover.

^ The CO level must drop briefly and then recover to its original value.

If the CO level recovers to its original value the oxygen sensor system is functioning properly.
If the CO level does not recover to its original value continue.

5. Reinstall the oil filler cap and turn the engine "OFF".
6. Disconnect the oxygen sensor harness connector.
7. Connect a jumper lead to the oxygen sensor harness connector (green wire) leading to the CIS-E control unit and ground it briefly.

^ The CO level should rise.

If the CO level rises, the oxygen sensor is defective. Replace the oxygen sensor.
If the CO level does not rise, the wiring harness or the CIS-E control unit may be defective.