Code No. P0073: No. 1 Intake Air Temperature Sensor Circuit High Input


OPERATION



  • A power voltage of 5 V is applied to the No.1 intake air temperature sensor output terminal (terminal No. 5) from the engine-ECU (terminal No. 62).
  • The power voltage is earthed to the engine-ECU (terminal No. 86) from the No. 1 intake air temperature sensor (terminal No. 4).

FUNCTION



  • The No. 1 intake air temperature sensor converts the intake air temperature into a voltage and inputs the voltage signal to the engine-ECU.
  • In response to the signal, the engine-ECU corrects the fuel injection amount, etc.
  • The No. 1 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.

TROUBLE JUDGMENT


Check Conditions
  • Battery positive voltage is 8 - 16 V
  • 2 seconds later after the ignition switch has been in "ON" position or the engine has started up.
Judgment Criterion
  • The No. 1 intake air temperature sensor output voltage is 4.9 V or more (the intake air temperature is below -40°C or equivalent).

FAIL-SAFE AND BACKUP FUNCTION



  • The intake air temperature is controlled to be 50°C.
  • The EGR control is stopped (fully closed).
  • The DPF regeneration is prohibited.
  • The AS&G control is prohibited.

PROBABLE CAUSES



  • Failed No. 1 intake air temperature sensor
  • Open circuit or harness damage in No. 1 intake air temperature sensor circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSTIC PROCEDURE

STEP 1. M.U.T.-III data list

  • Refer to Data List Reference Table .

  1. Item 43: No. 1 intake air temperature sensor
OK: At ambient temperature (atmospheric temperature) or equivalent.

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
Go to Step 2 .

STEP 2. Connector check: A-07 air flow sensor connector

Q. Is the check result normal?
Go to Step 3 .
Repair or replace the connector.

STEP 3. Check No. 1 intake air temperature sensor itself.

  • Check No. 1 intake air temperature sensor itself (Refer to ).

Q. Is the check result normal?
Go to Step 4 .
Replace the air flow sensor.

STEP 4. Perform voltage measurement at A-07 air flow sensor connector.

  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 5 and earth.
OK: 4.5 - 4.9 V

Q. Is the check result normal?
Go to Step 8 .
Go to Step 5 .

STEP 5. Connector check: B-09 engine-ECU connector

Q. Is the check result normal?
Go to Step 6 .
Repair or replace the connector.

STEP 6. Check harness between A-07 (terminal No. 5) air flow sensor connector and B-09 (terminal No. 62) engine-ECU connector.
note Before checking harness, check intermediate connector A-16, and repair if necessary.

  • Check output line for open circuit.

Q. Is the check result normal?
Go to Step 7 .
Repair the damaged harness wire.

STEP 7. M.U.T.-III data list

  • Item 43: No. 1 intake air temperature sensor
OK: At ambient temperature (atmospheric temperature) or equivalent.

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

STEP 8. Perform resistance measurement at A-07 air flow sensor connector.

  • Disconnect connector, and measure at harness side.
  • Resistance between terminal No. 4 and earth.
OK: Continuity (2 Ω or less)

Q. Is the check result normal?
Go to Step 11 .
Go to Step 9 .

STEP 9. Connector check: B-09 engine-ECU connector

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

STEP 10. Check harness between A-07 (terminal No. 4) air flow sensor connector and B-09 (terminal No. 86) engine-ECU connector.
note Before checking harness, check intermediate connector A-16, and repair if necessary.

  • Check earthing line for open circuit and damage.

Q. Is the check result normal?
Go to Step 7 .
Repair the damaged harness wire.

STEP 11. Connector check: B-09 engine-ECU connector

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

STEP 12. Check harness between A-07 (terminal No. 5) air flow sensor connector and B-09 (terminal No. 62) engine-ECU connector.
note Before checking harness, check intermediate connector A-16, and repair if necessary.

  • Check output line for damage.

Q. Is the check result normal?
Go to Step 7 .
Repair the damaged harness wire.