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Home >> Lexus >> 2002 >> GS 430 >> Repair and Diagnosis >> External Pages >> Different car >> Section 34 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0134: Oxygen Sensor Circuit No Activity Detected (Bank 1 Sensor 1) Or DTC P0154: Oxygen Sensor Circuit No Activity Detected (Bank 2 Sensor 1) >> Circuit Description
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Circuit Description

WARNING: This page is about a different car, the 2003 Lexus GS 300. However, it is still accessible from the selected car via links, so may be relevant.

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 oxygen sensor has the characteristic which 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 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 oxygen sensor informs the ECM of the LEAN condition (small electromotive force of greater than 0.45 volts). 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 is greater than 0.45 volts). 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, ECM is unable to perform accurate air-fuel ratio control. 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.

DTC is set when response time for heated oxygen sensor voltage output changes from rich to lean, or from lean to rich, in one second or more during idling after engine is warmed up. Possible causes are:

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