Oxygen Sensor Heater

HO2S Heater Wiring:

HO2S Heater Diagnostic Chart:

CIRCUIT DESCRIPTION:

The Oxygen (HO2S) has a built in heater. This heater has battery voltage whenever the ignition switch is turned "ON." The heater causes the H02S 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 H02S fails. However, since it is part of the H02S, 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/YEL wire of the four pin connector.

2. Checks the ground side of the circuit to the H02S heater.

3. This will check the heater element resistance. The 3.5 to 14.2 ohms range is at 23°C (73°F).

DIAGNOSTIC AIDS:

Check for poor connection and corrosion at the H02S connector for intermittent operation of the H02S heater circuit.