Standard Voltage

(d) Warm up the A/F sensor at an engine speed of 2,500 rpm for 90 seconds.

(e) On the tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / DATA LIST / USER DATA / AFS B1S1 and ENGINE SPD.

(f) Check the A/F sensor voltage three times, when the engine is in each of the following conditions:

(1) While idling (check for at least 30 seconds)

(2) At an engine speed of approximately 2,500 rpm (without any sudden changes in engine speed)

(3) Raise the engine speed to 4,000 rpm and then quickly release the accelerator pedal so that the throttle valve is fully closed.

Conditions

A/F Sensor Voltage Variations

Reference

(1) and (2)

Changes at approximately 3.3 V

3.1 V and 3.5 V

(3)

Increases to 3.8 V or more

This occurs during engine deceleration (when fuel-cut performed)

For more information, see the diagrams below.

Engine RPM

When A/F sensor circuit malfunctioning, voltage output does not change

Malfunction Condition:

(3) Approximately 4,000 rpm (2) Approximately 2,500 rpm

Engine RPM

A/F Sensor Voltage

1-r-LJ

(1) Idling \ 1

-11

i

/

Fuel-cut

When A/F sensor circuit malfunctioning, voltage output does not change

HINT:

• If the output voltage of the A/F sensor remains at approximately 3.3 V (see Malfunction Condition diagram) under any conditions, including those above, the A/F sensor may have an open circuit. (This will also happen if the A/F sensor heater has an open circuit.)

• If the output voltage of the A/F sensor remains at either approximately 3.8 V or more, or 2.8 V or less (see Malfunction Condition diagram) under any conditions, including those above, the A/F sensor may have a short circuit.

The ECM stops fuel injection (fuel cut) during engine deceleration. This causes a lean condition and results in a momentary increase in the A/F sensor output voltage. The ECM must establish a closed throttle valve position learning value to perform fuel cut. If the battery terminal has been reconnected, the vehicle must be driven over 10 mph (16 km/h) to allow the ECM to learn the closed throttle valve position. When the vehicle is driven:

The output voltage of the A/F sensor may be below 2.8 V during fuel enrichment. For the vehicle, this translates to a sudden increase in speed with the accelerator pedal fully depressed when trying to overtake another vehicle. The A/ F sensor is functioning normally.

The A/F sensor is a current output element; therefore, the current is converted into a voltage inside the ECM. Measuring the voltage at the connectors of the A/F sensor or ECM will show a constant voltage result.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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