Subaru Workshop Service and Repair Manuals

Oxygen Sensor Testing

CHECK ECU VOLTAGE AND OXYGEN SENSOR

1.

With engine completely warmed up and idling, measure voltage between ECU connector (F121)4 and ground.  Voltage should alternate between
0.3V and 0.6V.

2.

Disconnect oxygen sensor and measure voltage between sensor connector (F5)1 and ground.  Voltage should remain above .47 volts most of the
time.

Oxygen Sensor Harness Testing

CHECK ECU HARNESS

1.

With ignition "OFF," disconnect ECU and oxygen sensor connector.

2.

Measure resistance between ECU connector and oxygen sensor connector:

Connector & terminal:

Resistance:

(F121)4-(F5)1

Below 1 Ohm

3.

Connect ECU and oxygen sensor connectors.

4.

Measure resistance between ECU connector and ground:

Connector & terminal:

Resistance:

(F121)1-Ground

Below 10 Ohms

(F121)2-Ground

Below 10 Ohms