Heated Gas Oxygen (HEGO) Sensor

Vehicle may be equipped with one or 2 HEGO sensors. They are located in exhaust pipe, upstream of catalytic converters. Faults in sensor or circuit should set a service code. See QUICK TEST in TESTS W/CODES - EEC-IV article in the ENGINE PERFORMANCE section. If service code has not been set, ensure none of these conditions exist:

• Moisture inside sensor/harness connector.
• HEGO sensor coated with contaminants.
• Sensor circuit open or shorted to ground.

If necessary, see CIRCUIT TEST H in TESTS W/CODES - EEC-IV article in the ENGINE PERFORMANCE section for additional specifications and circuit testing procedures.