Circuit description
- The oxygen sensor is displayed in the DTCs, but these DTCs are related to the air/fuel ratio sensor.
- Sensor 1 means the sensor that is installed on the upstream (close to the engine) of the catalyst.
The air/fuel ratio sensor creates a voltage that corresponds to the actual air/fuel ratio.* The sensor voltage is used to provide the ECM with feedback for controlling the air/fuel ratio. The ECM determines the deviation from the stoichiometric air/fuel ratio level, and adjusts the fuel injection time. If there is a malfunction in the air/fuel ratio sensor, the ECM can no longer accurately control the air/fuel ratio.
The air/fuel ratio sensor is a planar type, and is one unit with the heater that heats the solid electrolyte (Zirconia material). This heater is controlled by the ECM. When the amount of air intake is low (the temperature of the exhaust gas is low), an electricity current flows to the heater, and the sensor is warmed up. This aids in accurately detecting the concentration of oxygen. Also, the sensor and heater part has become smaller than previous versions. The heat created by the heater is transferred to the solid electrolyte through alumina, and this aids in the sensor's operation.
The three-way catalytic converter is used to increase the purification rate of carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx), which are substances contained in the exhaust gas. To most efficiently use the three-way catalytic converter, it is necessary to precisely control the air/fuel ratio so that it is always near stoichiometric levels.
*: Values change inside the ECM. Because the air/fuel ratio sensor is a current output part, this electrical current is converted to voltage in the ECM. Measurements of the air/fuel sensor or ECM connectors display a certain voltage.
| DTC No. | DTC detection conditions | Faulty part |
|---|---|---|
| P2195 | In the air/fuel ratio feedback control, the rate of excess air (lambda) continuing for 10 seconds is 0.85 or less. (2 trips detection logic) |
|
| P2196 | In the air/fuel ratio feedback control, the rate of excess air (lambda) continuing for 10 seconds is 1.15 or more. (2 trips detection logic) |
- If these DTCs are recorded, using the SSM3 menu, check the air/fuel ratio sensor voltage output.
- The short-term fuel trim value can also be read with the SSM3.
- The ECM adjusts the voltage at the A1A+ and the A1A-terminals in the ECM to a certain level. Therefore, the voltage output of the air/fuel ratio sensor cannot be checked without using the SSM3.
- If a malfunction is detected in the air/fuel ratio sensor, the ECM records a DTC.