Troubleshooting

CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three-way catalytic converter is used, but for the most efficient use of the three-way catalytic converter, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio.
The oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the stoichiometric air/fuel ratio. This characteristic is used to detect the oxygen concentration in the exhaust gas and provide feedback to the computer for control of the air-fuel ratio.
When the air-fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the oxygen sensor informs the ECM of the LEAN condition (small electromotive force: 0 V).
When the air-fuel ratio is RICHER than the stoichiometric air-fuel ratio the oxygen concentration in the exhaust gas is reduced and the oxygen sensor informs the ECM of the RICH condition (large electromotive force: 1V).
The ECM judges by the electromotive force from the oxygen sensor whether the air-fuel ratio is RICH or LEAN and controls the injection time accordingly. However, if malfunction of the oxygen sensor causes output of abnormal electromotive force, the ECM is unable to perform accurate air-fuel ratio control.
The heated oxygen sensors include a heater which heats the Zirconia element. The heater is controlled by the ECM. When the intake air volume is low (the temperature of the exhaust gas is low) current flows to the heater to heat the sensor for accurate oxygen concentration detection.





DETECTING CONDITION

HINT:
Bank 1 refers to bank that includes cylinder No.1.
Bank 2 refers to bank that does not include cylinder No.1.
Sensor 1 refers to sensor closer to engine body.

Heated oxygen sensor's output voltage and short-term fuel trim value can be read using OBD II scan tool or LEXUS hand-held tester.





WIRING DIAGRAM

CONFIRMATION DRIVING PATTERN




(1) Connect LEXUS hand-held tester to the DLC3.
(2) Switch LEXUS hand-held tester from normal mode to check mode.
(3) Start engine and warm it up with all accessory switches OFF.
(4) Drive at 50 ~ 65 km/h (31 ~ 40 mph) for 1 ~ 3 minutes to warm up heated oxygen sensor.
(5) Let engine idle for 1 minute.

HINT: If a malfunction exists, the MIL will light up during step (5).

NOTICE:
- If conditions in this test are not strictly followed, detection of malfunction will not be possible.
- If you do not have a LEXUS hand-held tester, turn ignition switch OFF after performing steps (3) to (5) again.

INSPECTION PROCEDURE