Code No. P0102: Air flow Sensor Circuit Low Input

OPERATION

Power is supplied by the engine control relay (terminal No. 1) to the air flow sensor (terminal No. 5), and the air flow sensor (terminal No. 4) is earthed through the engine-ECU (terminal No. 71).
The air flow sensor (terminal No. 3) outputs a sensor signal, which is input into the engine-ECU (terminal No. 50).

FUNCTION

The air flow sensor outputs pulse signal that varies in accordance with the intake air volume.
In response to the signal, the engine-ECU controls exhaust gas recirculation control, etc.

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 air flow sensor output voltage is 0.50 V or less.

PROBABLE CAUSES

Failed air flow sensor
Short circuit in air flow 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 .

Item 114: Air flow sensor

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-32 air flow sensor connector

Q. Is the check result normal?

	Go to Step 3.

	Repair or replace the connector.

STEP 3. Perform voltage measurement at B-32 air flow sensor connector.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal No. 5 and earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 5.

	Go to Step 4.

STEP 4. Connector check: B-15X engine control relay connector

Q. Is the check result normal?

	Check intermediate connector D-113, and repair if necessary. If intermediate connector is normal, check and repair harness between B-15X (terminal No. 1) engine control relay connector and B-32 (terminal No. 5) air flow sensor connector. Check power supply for open/short circuit.

	Repair or replace the connector.

STEP 5. Perform resistance measurement at B-32 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 9.

	Go to Step 6.

STEP 6. Connector check: D-213 engine-ECU connector

Q. Is the check result normal?

	Go to Step 7.

	Repair or replace the connector.

STEP 7. Check harness between B-32 (terminal No. 4) air flow sensor connector and D-213 (terminal No. 71) engine-ECU connector.

Check earthing line for damage.

Q. Is the check result normal?

	Go to Step 8.

	Repair the damaged harness wire.

STEP 8. M.U.T.-III data list

Refer to Data List Reference Table .

Item 114: Air flow sensor

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 ).

STEP 9. Perform voltage measurement at B-32 air flow sensor connector.

Disconnect connector, and measure at harness side.
Voltage between terminal No. 3 and earth.

OK: 4.9 - 5.1 V

Q. Is the check result normal?

	Go to Step 12.

	Go to Step 10.

STEP 10. Connector check: D-213 engine-ECU connector

Q. Is the check result normal?

	Go to Step 11.

	Repair or replace the connector.

STEP 11. Check harness between B-32 (terminal No. 3) air flow sensor connector and D-213 (terminal No. 50) engine-ECU connector.

Check output line for short circuit.

Q. Is the check result normal?

	Replace the air flow sensor.

	Repair the damaged harness wire.

STEP 12. Perform voltage measurement at D-213 engine-ECU connector.

Measure engine-ECU terminal voltage.
Disconnect B-32 air flow sensor connector.
Ignition switch: ON
Voltage between terminal No. 50 and earth.

OK: 4.9 - 5.1 V

Q. Is the check result normal?

	Go to Step 14.

	Go to Step 13.

STEP 13. Connector check: D-213 engine-ECU connector

Q. Is the check result normal?

	Check and repair harness between B-32 (terminal No. 3) air flow sensor connector and D-213 (terminal No. 50) engine-ECU connector. Check output line for open circuit.

	Repair or replace the connector.

STEP 14. Connector check: D-213 engine-ECU connector

Q. Is the check result normal?

	Go to Step 8.

	Repair or replace the connector.