Heated Oxygen Sensor
HEATED OXYGEN SENSORDescription
The heated oxygen sensor senses the oxygen concentration in exhaust gas, converts it into a voltage which is sent to the engine control module. The heated oxygen sensor outputs about 800 mV when the air fuel ratio is richer than the theoretical ratio and outputs about 100 mV when the ratio is leaner (higher oxygen concentration in exhaust gas). The engine control module controls the fuel injection ratio based on this signal so that the air fuel ratio is maintained at the theoretical ratio.
Circuit Diagram
Troubleshooting Procedures
Troubleshooting Hints
1. If the heated oxygen sensor is defective abnormally high emissions occur.
2. If the heated oxygen sensor check has resulted normal but the sensor output voltage is out of specification, check for the following items related to air fuel ratio control system.
- Faulty injector
- Air leaks in the intake manifold.
- Faulty mass air flow sensor, engine coolant temperature sensor.
Using Voltmeter
Harness Inspection Procedure
Sensor Inspection Procedure
NOTE: Before checking, warm up the engine until the engine coolant temperature reaches 80 to 95° C (176 to 205° F). Use an accurate digital voltmeter.
1. Disconnect the heated oxygen sensor connector, and measure the resistance between terminal 1 and terminal 2.
At temperature 400° C (752° F),
Resistance: 30 ohms or more
2. Replace the oxygen sensor if there is a malfunction.