Code No. P0072: No. 2 Intake Air Temperature Sensor Circuit Low Input








OPERATION



  • A power voltage of 5 V is applied to the No. 2 intake air temperature sensor output terminal (terminal No. 1) from the engine-ECU (terminal No. 38).
  • The power voltage is earthed to the engine-ECU (terminal No. 32) from the No. 2 intake air temperature sensor (terminal No. 2).

FUNCTION



  • The No. 2 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. 2 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. 2 intake air temperature sensor output voltage is 0.05 V or less (the intake air temperature is above 150°C or equivalent).

PROBABLE CAUSES



  • Failed No. 2 intake air temperature sensor
  • Short circuit in No. 2 intake air temperature sensor circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSTIC PROCEDURE

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

  • Item 8: No. 2 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: B-128 No. 2 intake air temperature sensor connector

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

STEP 3. Check No. 2 intake air temperature sensor itself.

  • Check No. 2 intake air temperature sensor itself (Refer to ).

Q. Is the check result normal?
Go to Step 4 .
Replace the No. 2 intake air temperature sensor.

STEP 4. Perform voltage measurement at B-128 No. 2 intake air temperature sensor connector.

  • Disconnect connector, and measure at 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 8 .
Go to Step 5 .

STEP 5. Connector check: D-213 engine-ECU connector

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

STEP 6. Check harness between B-128 (terminal No. 1) No. 2 intake air temperature sensor connector and D-213 (terminal No. 38) engine-ECU connector.

  • Check output line for short 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 8: No. 2 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. When the engine-ECU is replaced, write the chassis number (Refer to GROUP 00 - Precautions Before Service - How to Perform Chassis Number Writing ). After replacing the engine-ECU, register the injector identification code and learn fuel injection (Refer to GROUP 00 - Precautions Before Service - What The Common Rail Engine Learns ). After registering the injector identification code, the vehicle equipped with the closed type DPF carries out the forcible DPF regeneration. (Refer to GROUP 17 - Diesel Particulate Filter (DPF) System - Forcible DPF Regeneration ).

STEP 8. Perform resistance measurement at B-128 No. 2 intake air temperature sensor connector.

  • Disconnect connector, and measure at harness side.
  • Resistance between terminal No. 2 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: D-213 engine-ECU connector

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

STEP 10. Check harness between B-128 (terminal No. 2) No. 2 intake air temperature sensor connector and D-213 (terminal No. 32) engine-ECU connector.

  • Check earthing line for damage.

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

STEP 11. Connector check: D-213 engine-ECU connector

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

STEP 12. Check harness between B-128 (terminal No. 1) No. 2 intake air temperature sensor connector and D-213 (terminal No. 38) engine-ECU connector.

  • Check output line for damage.

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