Oxygen Sensor: Testing and Inspection

Verify: That the engine is at normal operating temperatures.
The idle speed, timing 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.

Diaphragm Pressure Regulator Testing Connections:

1. Remove the differential pressure regulator harness connector.
2. Connect a suitable volt/ohm meter and test harness to the differential pressure regulator. Use a milliampere scale.
3. With the engine idling, check and record the current value.

Component Locations:

4. Clamp closed the crankcase breather hose.

^ The control current must decrease.

If the control current decreases the oxygen sensor system is functioning properly.
If the control current does not decrease, continue.

5. Remove the clamp from the crankcase breather hose.
6. Disconnect the oxygen sensor harness connector.
7. Connect a jumper lead to terminal 1 (green wire, spade terminal) of the CIS-E Motronic harness connector and ground it briefly.

^ The control current increases.

If the control current increases, the oxygen sensor is defective. Replace the oxygen sensor.
If the control current does not increase, the wiring harness or the CIS-E Motronic control unit may be defective.