Oxygen Sensor: Testing and Inspection

Fig. 5 Oxygen Sensor Heater Connector (Between fuel distributor and right fender):

Fig. 7 Differential Pressure Regulator Test Harness:

Note; Engine must be at normal operating temp. (80°C/176°F).
1. Connect test harness VW 1315A/1, between the differential pressure regulator and the harness plug.
2. Connect a multimeter to the test harness.
3. Disconnect the oxygen sensor wire from the green lead.
4. With engine at idle, ground the green lead. Differential pressure regulator current should increase to +10 mA.
a. If current does not increase, check wiring between the oxygen sensor connector and the injection control unit.
b. If the wiring is OK, replace the injection control unit.
5. Reconnect the oxygen sensor to the green wire and restart the engine.
6. Accelerate engine briefly to 3000 rpm to heat up the oxygen sensor. The differential pressure regulator current should return to its original value and should fluctuate slightly.
7. If the current reading is not as specified, replace the oxygen sensor.