Code No. P0072: Intake Air Temperature Sensor Circuit Low Input


OPERATION



  • A power voltage of 5 V is applied to the Intake air temperature sensor output terminal from the engine-ECU connector terminal ATS.
  • The power voltage is earthed to the engine-ECU connector terminal ATSE from the Intake air temperature sensor connector terminal.

FUNCTION



  • The 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 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 Intake air temperature sensor output voltage is 0.05 V or less (the intake air temperature is above 150°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 Intake air temperature sensor
  • Short circuit in Intake air temperature sensor circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSTIC PROCEDURE

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

  • Item 43: 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. Check Intake air temperature sensor itself.

  • Intake air temperature sensor connector check.
  • Check Intake air temperature sensor itself (Refer to ).

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

STEP 3. Perform Voltage measurement at air flow sensor connector.

  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal engine-ECU ATS line and body earth.
OK: 4.5 - 4.9 V

Q. Is the check result normal?
Go to Step 6.
Go to Step 4.

STEP 4. Check harness between air flow sensor connector terminal and engine-ECU connector terminal ATS.

  • Check output line for short circuit.

Q. Is the check result normal?

Go to Step 5.
Repair or replace the connector, or repair the damaged harness wire.

STEP 5. M.U.T.-III data list

  • Item 43: 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 6. Perform resistance measurement at air flow sensor connector.

  • Disconnect connector, and measure at harness side.
  • Resistance between terminal engine-ECU ATSE line and body earth.
OK: Continuity (2 Ω or less)

Q. Is the check result normal?
Go to Step 8.
Go to Step 7.

STEP 7. Check harness between air flow sensor connector terminal and engine-ECU connector terminal ATSE.

  • Check earthing line for damage.

Q. Is the check result normal?
Go to Step 5.
Repair or replace the connector, or repair the damaged harness wire.

STEP 8. Check harness between air flow sensor connector terminal and engine-ECU connector terminal ATS.

  • Check output line for damage.

Q. Is the check result normal?

Go to Step 5.
Repair or replace the connector, or repair the damaged harness wire.