Code No. P0102: Air Flow Sensor Circuit Low Input

OPERATION

Power is supplied by the engine control relay connector terminal to the air flow sensor connector terminal.
Power is supplied by the engine-ECU connector terminal AFS5 to the air flow sensor connector terminal, and the air flow sensor connector terminal is earthed through the engine-ECU connector terminal AFSE.
The air flow sensor connector terminal outputs a sensor signal, which is input into the engine-ECU connector terminal AFS.

FUNCTION

The air flow sensor outputs current that varies in accordance with the intake air volume.
The engine-ECU uses the amperage output by the air flow sensor and the engine speed signal in order to determine the basic injection duration of the injector.

TROUBLE JUDGEMENT

Check Condition

More than 3 seconds have passed since the ignition switch was turned to "ON" position.

Judgement Criterion

Air flow sensor output voltage is less than 0.2 V (corresponding to an air flow rate of 0 g/sec or less) for 2 seconds.

FAIL-SAFE AND BACKUP FUNCTION

Fuel control is carried out using throttle opening degree and engine speed in accordance with preset map.

PROBABLE CAUSES

Failed air flow sensor
Open/short circuit or harness damage in air flow sensor circuit or loose connector contact
Failed engine-ECU

DIAGNOSIS PROCEDURE

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

Data list reference table (Refer to ).

Item 10: 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. Perform voltage measurement at air flow sensor connector.

Disconnect connector, and measure at harness side.
Ignition switch: "ON"
Voltage between terminal power supply line and body earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 3.

	Repair or replace the connector, or check and repair harness between engine control relay connector terminal and air flow sensor connector terminal. Check power supply line for open/short circuit.

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

Use special tool test harness (MB991709) to connect connector, and measure at pick-up harness.
Ignition switch: "ON"
Voltage between terminal engine-ECU AFS5 line and body earth.

OK: 4.9 - 5.1 V

Q. Is the check result normal?

	Go to Step 5.

	Go to Step 4.

STEP 4. Perform voltage measurement at engine-ECU connector.

Measure engine-ECU connector terminal voltage.
Ignition switch: "ON"
Voltage between terminal AFS5 and body earth.

OK: 4.9 - 5.1 V

Q. Is the check result normal?

	Go to Step 5.

	Repair or replace the connector, or check and repair harness between engine-ECU connector terminal AFS5 and air flow sensor connector terminal. Check power supply line for open/short circuit.

STEP 5. Check of open circuit, and short circuit in AFS line between air flow sensor connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 6.

	Repair the connector(s) or wiring harness.

STEP 6. Check of damage in power supply line between engine control relay connector and air flow sensor connector.

Q. Is the check result normal?

	Go to Step 7.

	Repair the connector(s) or wiring harness.

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

Data list reference table (Refer to ).

Item 10: 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 8.

STEP 8. Replace the air flow sensor

After replacing the air flow sensor, reconfirm whether the diagnosis code is set.

Q. Is the diagnosis code set?

	Replace the engine-ECU.

	Check end.