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Home >> Lexus >> 2003 >> SC 430 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0133 Or DTC P0153 >> Circuit Description
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Circuit Description

To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a 3-way catalytic converter is used. But for the most efficient use of the 3-way catalytic converter, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio. The heated oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the stoichiometric air-fuel ratio. This is used to detect the oxygen concentration in the exhaust gas and provide the ECM with feedback to control the air-fuel ratio. When the air-fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases, and the heated oxygen sensor informs the ECM of the LEAN condition (small electromotive force of greater than 0.45 volt). When the air-fuel ratio is RICHER than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is reduced, and the heated oxygen sensor informs the ECM of the RICH condition (large electromotive force is greater than 0.45 volt). The ECM judges by the electromotive force from the heated oxygen sensor whether the air-fuel ratio is RICH or LEAN and controls the injection time accordingly. However, if the malfunction of the oxygen sensor causes an output of abnormal electromotive force, the ECM becomes unable to perform the accurate air-fuel ratio control. The main 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 (temperature of the exhaust gas is low), current flows to the heater in order to heat the sensor for the accurate oxygen concentration detection.

DTC P0133 is for bank 1, sensor 1. DTC P0153 is for bank No. 2, sensor 1. See Figure and Figure . DTC is set when engine is warmed up and idling if ECM detects a response time of one second or more for sensor to change from rich to lean, or lean to rich. Possible causes are:

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