Inspection Procedure 8: Fuel Temperature Sensor System








OPERATION



  • A power voltage of 5 V is applied to the fuel temperature sensor output terminal (terminal No. 1) from the engine-ECU (terminal No. 24).
  • The power voltage is earthed to the engine-ECU (terminal No. 25) from the fuel temperature sensor (terminal No. 2).

FUNCTION



  • The fuel temperature sensor converts the fuel 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 to suit the fuel temperature.
  • The fuel temperature sensor is a kind of resistor, which has characteristics to reduce its resistance as the fuel temperature rises. Therefore, the sensor output voltage varies with the fuel temperature, and becomes lower as the fuel temperature rises.

PROBABLE CAUSE



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

DIAGNOSIS PROCEDURE

STEP 1. Connector check: B-11 fuel temperature sensor connector

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

STEP 2. Perform resistance measurement at B-11 fuel temperature sensor connector.

  • Disconnect connector, and measure at the harness side.
  • Voltage between terminal No. 2 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-05 engine-ECU connector

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

STEP 4. Check harness between B-11 (terminal No. 2) fuel temperature sensor connector and B-05 (terminal No. 25) 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 B-11 fuel temperature sensor connector.

  • Disconnect connector, and measure at the harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 1 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-05 engine-ECU connector.

  • Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB992044) to measure at connector for inspection.
  • Disconnect B-11 fuel temperature sensor connector.
  • Ignition switch: ON
  • Voltage between terminal No. 24 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-05 engine-ECU connector

Q. Is the check result normal?

    Check and repair harness between B-11 (terminal No. 1) fuel temperature sensor connector and B-05 (terminal No. 24) engine-ECU connector.

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

STEP 9. Connector check: B-05 engine-ECU connector

Q. Is the check result normal?

Go to Step 10 .
Repair or replace the connector.

STEP 10. Check harness between B-11 (terminal No. 1) fuel temperature sensor connector and B-05 (terminal No. 24) 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-05 engine-ECU connector

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

STEP 12. Check harness between B-11 (terminal No. 1) fuel temperature sensor connector and B-05 (terminal No. 24) 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 fuel temperature sensor.

  • After replacing the fuel temperature sensor, re-check the trouble symptoms.

Q. Does trouble symptom persist?

Replace the engine-ECU.
The check is end.