California Models

DIAGNOSTIC PROCEDURE

Wiring Diagram Of The Oxygen Sensor Circuit:

NOTE: If Diagnostic Trouble Code "21" is output inspect / replace front Oxygen Sensor. If Diagnostic Trouble Code "28" is output, inspect / replace rear Oxygen Sensor.

1. Check voltage of terminals HT1, HT2.
- If OK proceed to step 3.
- If not OK proceed to step 2.
2. Check resistance of Main Heated Oxygen Sensor heater.
- If OK check and repair Main Heated Oxygen Sensor heater circuit.
- If not OK replace Main Heated Oxygen Sensor.
3. Check operation of Main Heated Oxygen Sensor heater.
- If OK replace Main Heated Oxygen Sensor.
- If not OK check and replace Engine Control Module.