Circuit Description

WARNING: This page is about a different car, the 2004 Toyota RAV4. However, it is still accessible from the selected car via links, so may be relevant.

The A/F sensor provides output voltage* approximately equal to the existing air-fuel ratio. The A/F sensor output voltage is used to provide feedback for the ECM to control the air-fuel ratio.

With the A/F sensor output, the ECM can determine deviation from the stoichiometric air-fuel ratio and control proper injection time. If the A/F sensor is malfunctioning, the ECM is unable to accurately control air-fuel ratio.

The A/F sensor is equipped with a heater which heats the zirconia element. The heater is also controlled by the ECM. When the intake air volume is low (the temperature of the exhaust gas is low), current flows to the heater witch heats the sensor to facilitate detection of accurate oxygen concentration.

The A/F sensor is a planar type. Compared to a conventional type, the sensor and heater portions are narrower. Because the heat of the heater is conducted through the alumina to zirconia (of the sensor portion), sensor activation is accelerated.

To obtain a high purification rate of the CO, HC and NOx components of the exhaust gas, a three-way catalytic converter is used. The converter is most efficient when the air-fuel ratio is maintained near the stoichiometric air-fuel ratio.

*: The voltage value changes in the inside of the ECM only.

Fig 1: Identifying A/F Sensor

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: DTC (P2195, P2196) Diagnosis Table

HINT:

DTCs P2195 and P2196 indicate a malfunction related to bank 1 of the A/F sensor circuit.
Sensor 1 refers to the sensor closest to the engine assembly.
After confirming DTCs P2195 and P2196, use the hand-held tester or the OBD II scan tool to confirm A/F sensor output voltage (AFS B1S1) from the All menu (to reach the ALL menu: DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL).
The A/F sensor's output voltage and the short-term fuel trim value can be read using the OBD II scan tool or the hand-held tester.
The ECM controls the voltage of the A1A+ and A1A- terminals of the ECM to a fixed voltage. Therefore, it is impossible to confirm the A/F sensor output voltage without the OBD II scan tool or the handheld tester.
The OBD II scan tool (excluding hand-held tester) displays one fifth of the A/F sensor output voltage which is displayed on the hand-held tester.