Code No. P0073: No. 2 Intake Air Temperature Sensor Circuit High 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 fuel 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 4.9 V or more (the intake air temperature is below -40°C or equivalent).

FAIL-SAFE AND BACKUP FUNCTION

No. 2 intake air temperature is controlled as 50°C.
Exhaust gas recirculation control is stopped (fully closed).

PROBABLE CAUSES

Failed No. 2 intake air temperature sensor
Open circuit or harness damage in No. 2 intake air temperature sensor circuit or loose connector contact
Failed engine-ECU

DIAGNOSIS 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: A-104 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 A-104 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: C-116 engine-ECU connector

Q. Is the check result normal?

	Go to Step 6 .

	Repair or replace the connector.

STEP 6. Check harness between A-104 (terminal No. 1) No. 2 intake air temperature sensor connector and C-116 (terminal No. 38) engine-ECU connector.

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 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. 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 ).

STEP 8. Perform resistance measurement at A-104 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: C-116 engine-ECU connector

Q. Is the check result normal?

	Go to Step 10 .

	Repair or replace the connector.

STEP 10. Check harness between A-104 (terminal No. 2) No. 2 intake air temperature sensor connector and C-116 (terminal No. 32) engine-ECU connector.

Check earthing line for open circuit.

Q. Is the check result normal?

	Go to Step 7 .

	Repair the damaged harness wire.

STEP 11. Connector check: C-116 engine-ECU connector

Q. Is the check result normal?

	Go to Step 12 .

	Repair or replace the connector.

STEP 12. Check harness between A-104 (terminal No. 1) No. 2 intake air temperature sensor connector and C-116 (terminal No. 38) engine-ECU connector.

Check output for damage.

Q. Is the check result normal?

	Go to Step 7 .

	Repair the damaged harness wire.