Inspection Procedure 5: Air Temperature Sensor System








OPERATION



  • A power voltage of 5 V is applied to the air temperature sensor output terminal (terminal No. 2) from the engine-ECU (terminal No. 22).
  • The power voltage is earthed to the engine-ECU (terminal No. 10) from the air temperature sensor (terminal No. 3).

FUNCTION



  • The air temperature sensor converts the intake air temperature into a voltage signal, and inputs the voltage to the engine-ECU.
  • Role of the engine-ECU in relation to the information received is to correct the air flow.
  • The air temperature sensor is a kind of resistor, which has characteristics to reduce its resistance as the intake air temperature rises. Therefore, the sensor output voltage varies with the intake air temperature, and becomes lower as the intake air temperature rises.

PROBABLE CAUSES



  • Failed air temperature sensor
  • Open/short circuit or harness damage in air temperature sensor circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: A-08 air flow sensor connector

Q. Is the check result normal?
Go to Step 2 .
Repair or replace the connector.

STEP 2. Perform resistance measurement at A-08 air flow sensor connector.

  • Disconnect connector, and measure at the harness side.
  • Resistance between terminal No. 3 and earth.
OK: Continuity (2 Ω or less)

Q. Is the check result normal?
Go to Step 6 .
Go to Step 3 .

STEP 3. Connector check: B-18 engine-ECU connector

Q. Is the check result normal?
Go to Step 4 .
Repair or replace the connector.

STEP 4. Check harness between A-08 (terminal No. 3) air flow sensor connector and B-18 (terminal No. 10) engine-ECU connector.

  • Check earthing line for open circuit and damage.

Q. Is the check result normal?
Go to Step 5 .
Repair the damaged harness wire.

STEP 5. Check the trouble symptoms.

Q. Does trouble symptom persist?

Replace the engine-ECU.
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

STEP 6. Perform voltage measurement at A-08 air flow sensor connector.

  • Disconnect connector, and measure at the harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 2 and earth.
OK: 4.5 - 4.9 V

Q. Is the check result normal?
Go to Step 9 .
Go to Step 7 .

STEP 7. Connector check: B-18 engine-ECU connector

Q. Is the check result normal?

Go to Step 8 .
Repair or replace the connector.

STEP 8. Check harness between A-08 (terminal No. 2) air flow sensor connector and B-18 (terminal No. 22) engine-ECU connector.

  • Check output line for open/short circuit.

Q. Is the check result normal?
Go to Step 5 .
Repair the damaged harness wire.

STEP 9. Connector check: B-18 engine-ECU connector

Q. Is the check result normal?
Go to Step 10 .
Repair or replace the connector.

STEP 10. Check harness between A-08 (terminal No. 2) air flow sensor connector and B-18 (terminal No. 22) engine-ECU connector.

  • Check output line for damage.

Q. Is the check result normal?
Go to Step 11 .
Repair or replace the connector.

STEP 11. Replace the air flow sensor.

  • After replacing the air flow sensor, re-check the trouble symptoms.

Q. Does trouble symptom persist?

Replace the engine-ECU.
The check is end.