Inspection Procedure 5: Intake Air Temperature Sensor System








OPERATION



  • A power voltage of 5 V is applied to the intake air temperature sensor output terminal (terminal No. 3) from the engine-ECU (terminal No. 120).
  • The power voltage is earthed to the engine-ECU (terminal No. 70) from the intake air temperature sensor (terminal No. 4).

FUNCTION



  • The intake air temperature sensor converts the intake air temperature into a voltage signal, and inputs the voltage to the engine-ECU.
  • In response to the signal, the engine-ECU controls the fuel injection quantity and the boost pressure control.
  • The intake 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 CAUSE



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

DIAGNOSIS PROCEDURE

STEP 1. Connector check: A-41 boost pressure sensor connector

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

STEP 2. Perform resistance measurement at A-41 boost pressure sensor connector.

  • Disconnect connector, and measure at the harness side.
  • Resistance between terminal No. 4 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-06 engine-ECU connector

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

STEP 4. Check harness between A-41 (terminal No. 4) boost pressure sensor connector and B-06 (terminal No. 70) 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-41 boost pressure sensor connector.

  • Disconnect connector, and measure at the harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 3 and earth.
OK: 4.5 - 4.9 V

Q. Is the check result normal?
Go to Step 11 .
Go to Step 7 .

STEP 7. Perform voltage measurement at B-06 engine-ECU connector.

  • Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB992044) to measure at connector for inspection.
  • Disconnect A-41 boost pressure sensor connector.
  • Ignition switch: ON
  • Voltage between terminal No. 120 and earth.
OK: 4.5 - 4.9 V

Q. Is the check result normal?
Go to Step 8 .
Go to Step 9 .

STEP 8. Connector check: B-06 engine-ECU connector

Q. Is the check result normal?

    Check and repair harness between A-41 (terminal No. 3) boost pressure sensor connector and B-06 (terminal No. 120) engine-ECU connector.

    • Check output line for open circuit.
Repair or replace the connector.

STEP 9. Connector check: B-06 engine-ECU connector

Q. Is the check result normal?

Go to Step 10 .
Repair or replace the connector.

STEP 10. Check harness between A-41 (terminal No. 3) boost pressure sensor connector and B-06 (terminal No. 120) engine-ECU connector.

  • Check output line for short circuit.

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

STEP 11. Connector check: B-06 engine-ECU connector

Q. Is the check result normal?
Go to Step 12 .
Repair or replace the connector.

STEP 12. Check harness between A-41 (terminal No. 3) boost pressure sensor connector and B-06 (terminal No. 120) engine-ECU connector.

  • Check output line for damage.

Q. Is the check result normal?
Go to Step 13 .
Repair or replace the connector.

STEP 13. Replace the boost pressure sensor.

  • After replacing the boost pressure sensor, re-check the trouble symptoms.

Q. Does trouble symptom persist?

Replace the engine-ECU.
The check is end.