Description

The A/F sensor generates a voltage* that corresponds to the actual air-fuel ratio. This sensor voltage is used to provide the ECM with feedback so that it can control the air-fuel ratio. The ECM determines the deviation from the stoichiometric air-fuel ratio level, and regulates the fuel injection time. If the A/F sensor malfunctions, the ECM is unable to control the air-fuel ratio accurately.

The A/F sensor is of the planar type and is integrated with the heater, which heats the solid electrolyte (zirconia element). This heater is controlled by the ECM. When the intake air volume is low (the exhaust gas temperature is low), a current flows into the heater to heat the sensor, in order to facilitate accurate air-fuel ratio detection. In addition, the sensor and heater portions are narrower than the conventional type. The heat generated by the heater is conducted to the solid electrolyte through the alumina, therefore the sensor activation is accelerated.

In order to obtain a high purification rate of the carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) components in the exhaust gas, a TWC is used. For the most efficient use of the TWC, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric level. *: Value changes inside the ECM. Since the A/F sensor is the current output element, a current is converted into a voltage inside the ECM. Any measurements taken at the A/F sensor or ECM connectors will show a constant voltage.

Element

Exhaust Gas

Element

Exhaust Gas

Cover

Alumina

Heater

Solid Electrolyte (Zirconia Element)

Platinum Electrode

Atmospheric Air

Alumina

Heater

Solid Electrolyte (Zirconia Element)

ECM Monitored A/F Sensor Voltage

Platinum Electrode

Atmospheric Air

12 13 14 15 16 17 18

Air-Fuel Ratio

A-A Cross Section

DTC No.

DTC Detection Conditions

Trouble Areas

P2195

Conditions (a) and (b) continue for 10 seconds or more (2 trip detection logic):

(a) A/F sensor voltage more than 3.8 V

(b) Heated Oxygen (HO2) sensor voltage 0.15 V or more

• Open or short in A/F sensor (sensor 1) circuit

• Integration relay (EFI MAIN relay)

• A/F sensor heater and EFI MAIN relay circuits

• ECM

While fuel-cut operation performed (during vehicle deceleration), A/F sensor current 3.6 mA or more for 3 seconds (2 trip detection logic)

• ECM

P2196

Conditions (a) and (b) continue for 10 seconds or more (2 trip detection logic):

(a) A/F sensor voltage less than 2.8 V for 10 seconds

(b) HO2 sensor voltage less than 0.6 V

• Open or short in A/F sensor (sensor 1) circuit

• Integration relay (EFI MAIN relay)

• A/F sensor heater and EFI MAIN relay circuits

• ECM

While fuel-cut operation performed (during vehicle deceleration), A/F sensor current less than 1.0 mA for 3 seconds (2 trip detection logic)

• When either of these DTCs is set, check the A/F sensor output voltage by selecting the following menu items on the intelligent tester: DIAGNOSIS / ENHANCED OBD II / DATA LIST / PRIMARY / AFS B1 S1.

• Short-term fuel trim values can also be read using the intelligent tester.

• The ECM regulates the voltages at the A1A+ and A1A- terminals of the ECM to a constant level. Therefore, the A/F sensor output voltage cannot be confirmed without using the intelligent tester.

• If the A/F sensor is malfunctioning, the ECM sets the DTC P2195 or P2196.

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Do It Yourself Car Diagnosis

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