Oxygen Sensor: Testing and Inspection

Chart C-1A:

Oxygen Sensor Heater Circuit:

CIRCUIT DESCRIPTION:

The Oxygen (O2) has a built in heater. This heater has battery voltage whenever the ignition switch is turned "ON." The heater causes the O2 sensor to produce a signal to the ECM. This allows for better fuel control during engine warm-up. No codes can be set if the heater portion of the O2 sensor fails. However, since it is part of the O2 sensor, it is necessary to replace the entire sensor if the heater is found to be faulty.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. This checks for ignition voltage on BLK/WHT wire at the O2 sensor.

2. Checks the ground side of the circuit to the O2 heater.

3. This will check the heater element resistance. The 3 to 5.5 ohms range is at 23°C (73°F).

DIAGNOSTIC AIDS:

Check for poor connection and corrosion at the O2 connector for intermittent operation of the O2 heater circuit.