Toyota 2GR-FE Manual page 279

DTC P0037
DTC P0038
DTC P0057
DTC P0058
DTC P0141
DTC P0161
DESCRIPTION
A three-way catalytic converter (TWC) is used in order to convert the carbon monoxide (CO), hydrocarbon
(HC), and nitrogen oxide (NOx) into less harmful substances. To allow the TWC to function effectively, it is
necessary to keep the air-fuel ratio of the engine near the stoichiometric air-fuel ratio. For the purpose of
helping the ECM to deliver accurate air-fuel ratio control, a Heated Oxygen (HO2) sensor is used.
The HO2 sensor is located behind the TWC, and detects the oxygen concentration in the exhaust gas.
Since the sensor is integrated with the heater that heats the sensing portion, it is possible to detect the
oxygen concentration even when the intake air volume is low (the exhaust gas temperature is low).
When the air-fuel ratio becomes lean, the oxygen concentration in the exhaust gas becomes rich. The
HO2 sensor informs the ECM that the post-TWC air-fuel ratio is lean (low voltage, i.e. less than 0.45 V).
Conversely, when the air-fuel ratio is richer than the stoichiometric air-fuel level, the oxygen concentration
in the exhaust gas becomes lean. The HO2 sensor informs the ECM that the post-TWC air-fuel ratio is
rich (high voltage, i.e. more than 0.45 V). The HO2 sensor has the property of changing its output voltage
drastically when the air-fuel ratio is close to the stoichiometric level.
The ECM uses the supplementary information from the HO2 sensor to determine whether the air-fuel ratio
after the TWC is rich or lean, and adjusts the fuel injection time accordingly. Thus, if the HO2 sensor is
working improperly due to internal malfunctions, the ECM is unable to compensate for deviations in the
primary air-fuel ratio control.
2GR-FE ENGINE CONTROL SYSTEM – SFI SYSTEM
Oxygen Sensor Heater Control Circuit Low
(Bank 1 Sensor 2)
Oxygen Sensor Heater Control Circuit High
(Bank 1 Sensor 2)
Oxygen Sensor Heater Control Circuit Low
(Bank 2 Sensor 2)
Oxygen Sensor Heater Control Circuit High
(Bank 2 Sensor 2)
Oxygen Sensor Heater Circuit Malfunction
(Bank 1 Sensor 2)
Oxygen Sensor Heater Circuit Malfunction
(Bank 2 Sensor 2)
ES–123
ES