Oxygen Sensor: Testing and Inspection

OXYGEN SENSOR (O2S)







DESCRIPTION
The Heated Oxygen Sensor (HO2S) is used to supply the ECM with information regarding the composition of the air/fuel mixture. To measure the oxygen content, the HO2S requires a supply of ambient air as a reference. The HO2S produces a voltage that varies between 0.1 V and 0.9 V under normal operating conditions. The Engine Control Module (ECM) monitors this voltage and determines if the exhaust gas is lean or rich. If the voltage input at the ECM is under approx. 0.45 V, the exhaust is lean, and if the voltage input is over approx. 0.45 V, the exhaust is rich. The ECM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pluse width as necessary. The rear heated oxygen sensor is mounted on the rear side of the Catalytic (warm-up catalytic converter) or in the rear exhaust pipe. It detects the catalyst efficiency. The rear heated oxygen sensor (HO2S) produces a voltage between 0 V and 1 V. This rear heated oxygen sensor is used to estimate the oxygen storage capacity. If a catalyst has good conversion properties, the oxygen fluctuations are smoothed by the oxygen storage capacity of the catalyst. If the conversion provided by the catalyst is low due to engine, poisoning or misfiring, then the oxygen fluctuations sre similar to signals from the front oxygen sensor.

Circuit Diagram:

CIRCUIT DIAGRAM

Signal Waveform:

SIGNAL WAVEFORM

HARNESS INSPECTION
Refer to DTC P0030, P0031, P0032, P0036 - P0038, P0130, P0131, P0132, P0133, P0134 and P0136 - P0140 troubleshooting procedures.

SENSOR INSPECTION
1. Engine starts and Check signals of front and rear HO2S. (Refer to "SIGNAL WAVEFORM")




2. Measure resistance between the terminals 3 and 4 of front and rear HO2S connectors.

Specification : 3.3 - 4.1 Ohms at 20 °C (68 °F)

CAUTION: When disassembling sensor, remove smoothly by hand right after loosening toque.