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Hino P0104 Fault Code: Air Flow Sensor – Out Of Range

30/11/2024

Technical description

The air flow sensor installed to the air cleaner consistently measures an intake air volume

Description of malfunction

The air flow sensor value cannot be correctly recognized

Dtc set condition

Check Conditions:

Starter switch ON
Battery voltage is in the range of 10V to 16V
Engine speed is at least 725 r/min
The conditions described above remain for 5 seconds or longer

Judgment Criteria:

Output of the air flow sensor remains less than 2.0 kHz (3.9 kg/h) for 3 seconds or longer

Reset condition

After normal operation is restored and the starter switch is turned to LOCK

Indication, warning or system control

Regulation when the dtc is set

MIL: ON
SVS light: OFF
Engine output is restricted

Symptoms on the vehicle when the dtc is set

Symptoms on the vehicle due to backup control (fail safe function):

Engine output is insufficient

Pre-inspection work

Check that the battery voltage is in the normal range.

After-inspection work

Clear all past DTCs

Check that no DTC is stored after test drive

Possible causes

Sensor disconnected from the measured part or sensing unit malfunctioning (due to dirt, clogging, damage, etc.)
Engine ECU sensor power supply (air flow sensor dedicated 12 V power supply) malfunction or internal circuit malfunction
Sensor harness disconnection, short-circuit
Poor connector contact or faulty connector fit
Sensor harness high frequency noise

Inspection procedure

Troubleshooting steps

Step 1: Check the DTC detected (Engine ECU) 1 [Diagnostic Tool]

Set the starter switch to the “LOCK” position.
Connect the vehicle to the diagnostic tool.
Set the starter switch to the “ON” position.
Select [Engine] and check if any DTC other than P0104 (for example, P0642, P0643, P0652, P0653) has been detected.

NOTE: Due to sensor power supply failures, P0104 may have been detected. First perform the diagnostic related to the sensor power supply

Has a DTC other than P0104 been detected?

Yes	Go to the diagnostic procedure of a related DTC
No	Go to Step 2

Step 2: Inspect the air flow sensor connector

Check the connection of the air flow sensor connector (Looseness and poor contact)

Were any failures found?

Yes

Connect securely, repair if needed. Clear all past DTCs. Check that no DTC is detected

after test drive

Go to Step 3

Step 3: Inspect the air flow sensor.

Check the installation of the air flow sensor
Make sure there is no dirt or damage to the air flow sensor

Were any failures found?

Yes	If dirt, clogging or damage was found in sensing unit, replace the air flow sensor. Clear all past DTCs. Check that no DTC is detected after test drive
No	Go to Step 4

Step 4: Inspect for short-circuit of the air flow sensor harness

Set the starter switch to the “LOCK” position.
Connect the signal check harness to the engine ECU vehicle-side harness. (Do not connect the harness to the ECU)
Disconnect the air flow sensor connector
Use the electrical tester to measure the resistance between the terminals of the engine ECU (signal check harness) and ground

MEASUREMENT CONDITIONS

TESTER CONNECTIONS

STANDARD VALUES

Starter switch: LOCK

Engine ECU (signal check

harness)

AFSI(E74) – Ground

AG4(E78) – Ground

AFVB(E12) – Ground

∞ Ω

Do the measurements meet the standard value?

Yes	Go to Step 5
No	Repair or replace the harness. Clear all past DTCs. Check that no DTC is detected after test drive.

Step 5: Inspect disconnection of the air flow sensor harness

Use the electrical tester to measure the resistance between the terminals of the engine ECU (signal check harness) and air flow sensor vehicle-side connector

MEASUREMENT CONDITIONS

TESTER CONNECTIONS

STANDARD VALUES

Starter switch: LOCK

Engine ECU (signal check

harness) – Air flow sensor vehicle-side connector

AFSI(E74) – AFSG

AG4(E78) – AFGD

AFVB(E12) – AFVB

1 Ω or less

Do the measurements meet the standard value?

Yes	Go to Step 6
No	Repair or replace the harness. Clear all past DTCs. Check that no DTC is detected after test drive.

Step 6: Inspect the air flow sensor power supply

Connect the signal check harness to the engine ECU
Set the starter switch to the “ON” position
Use the electrical tester to measure the voltage between the terminals of the air flow sensor vehicleside connector

MEASUREMENT CONDITIONS

TESTER CONNECTIONS

STANDARD VALUES

Starter switch: ON

Air flow sensor vehicle-side connector

AFVB – AFGD

4.5 – 5.5 V

Do the measurements meet the standard value?

Yes	Go to Step 7
No	Replace the engine ECU. Clear all past DTCs. Check that no DTC is detected after test drive.

Step 7: Inspect the air flow sensor signal

Set the starter switch to the “LOCK” position
Connect the air flow sensor connector
Start the engine
Use the oscilloscope to measure the signal voltage between the terminals in the engine ECU (signal check harness)

MEASUREMENT CONDITIONS

TESTER CONNECTIONS

STANDARD VALUES

After engine warm-up,

with engine idling

Engine ECU (signal check harness)

AFSI(E74) – AG4(E78)

5 – 6 kHz

Do the measurements meet the standard value?

Yes	Go to Step 8
No	Replace the air flow sensor. Clear all past DTCs. Check that no DTC is detected after test drive.

Step 8: Check the DTC detected (Engine ECU) 2 [Diagnostic Tool]

Perform engine warm-up. (Engine coolant temperature: 60°C {140°F} or more)
Stop the engine and set the starter switch to the “ON” position
Select [Engine] and check if P0104 has been detected

Has DTC P0104 been detected?

Yes	Replace the engine ECU. Clear all past DTCs. Check that no DTC is detected after test drive.
No	Procedure complete. Clear all past DTCs. Check that no DTC is detected after test drive.

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