Text in Illustration
(d) Reconnect the heated oxygen sensor connector.
(e) Reconnect the ECM connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR (HEATED OXYGEN SENSOR - ECM)
OK -- REPLACE ECM See: Powertrain Management/Computers and Control Systems/Engine Control Module/Service and
Repair/Removal
Up to 08/2009
2GR-FE ENGINE CONTROL: SFI SYSTEM: P0037,P0038,P0057,P0058,P0141,P0161: Oxygen Sensor Heater Control Circuit Low (Bank
1 Sensor 2)
P0161 - Oxygen Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)
DESCRIPTION
A three-way catalytic converter is used in order to convert the carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx) into less
harmful substances. To allow the three-way catalytic converter 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 sensor is used.
The heated oxygen sensor is located behind the three-way catalytic converter, 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 heated oxygen sensor informs the ECM that the
post-three-way catalytic converter 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
heated oxygen sensor informs the ECM that the post-three-way catalytic converter air fuel ratio is rich (high voltage, i.e. more than 0.45 V). The
heated oxygen 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 heated oxygen sensor to determine whether the air fuel ratio after the three-way catalytic
converter is rich or lean, and adjusts the fuel injection time accordingly. Thus, if the heated oxygen sensor is working improperly due to internal
malfunctions, the ECM is unable to compensate for deviations in the primary air fuel ratio control.
HINT
- Sensor 2 refers to the sensor mounted behind the three-way catalytic converter and located far from the engine assembly.
- When any of these DTCs are set, the ECM enters fail-safe mode. The ECM turns off the heated oxygen sensor heater in
fail-safe mode. Fail-safe mode continues until the engine switch is turned off.
- The ECM provides a pulse width modulated control circuit to adjust the current through the heater. The heated oxygen sensor
heater circuit uses a relay on the +B side of the circuit.
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