Error code News Shared knowledge

Hino P0401 Fault Code: EGR Low Flow

25/02/2025

Mục lục

TECHNICAL DESCRIPTION

The measured EGR rate, which is calculated from the air flow sensor, boost pressure sensor, and intake air temperature sensor (intake manifold), is compared with the predicted EGR rate, and malfunction is detected.

DTC SET CONDITION

DTC Detection Condition:

Either the fuel injection quantity is 15 – 100 mm3/st. cyl. with an engine speed of 2,000 – 2,250 r/min, or the quantity is 30 – 90 mm3/st. cyl. with an engine speed of 2,250 – 2,500 r/min
Engine speed fluctuation ≤ 117 r/min/sec
Fuel injection quantity fluctuation ≤ 53 mm3/st. cyl. sec
Predicted EGR flow quantity ≥ 40 g/sec.
Atmospheric pressure ≥ 75 kPa {10.8 psi}

Judgment Criteria:

The value of parameters calculated from the measured EGR rate, predicted EGR rate, and EGR valve feedback quantity is at least 0.2

RESET CONDITION

After normal operation is restored and the starter switch is turned OFF

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

Symptoms on the Vehicle Due to Malfunction:

Turbocharger noise or damage
Abnormal consumption of DEF solution

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

Obstruction due to buildup of soot or foreign substances in inlet/outlet of EGR cooler gas passageway
Obstruction due to buildup of soot or foreign substances in EGR valve
Malfunction of intake system
Air flow sensor failure
Boost pressure sensor failure
Intake air temperature sensor (intake manifold) failure
SCV failure
Injector failure

INSPECTION PROCEDURE

TROUBLESHOOTING STEPS

Step 1: Inspect the air cleaner element

Check the air cleaner element for dirt, clogging, or damage
Make sure the element is an OEM genuine part

Were any failures found?

Yes	Clean or replace the air cleaner element. Clear all past DTCs. Check that no DTC is detected after test drive
No	Go to Step 2

Step 2: 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 damaged, replace the air flow sensor. Clear all past DTCs. Check that no DTC is detected after test drive
No	Go to Step 3

Step 3: Inspect the boost pressure sensor

Check the installation of the boost pressure sensor
Make sure there is no dirt or damage to the boost pressure sensor

Were any failures found?

Yes	Clean the boost pressure sensor and install it properly. If damaged, replace the boost pressure sensor. Clear all past DTCs. Check that no DTC is detected after test drive.
No	Go to Step 4

Step 4) Check the boost pressure sensor output signal [Diagnostic Tool].

Set the starter switch to the “LOCK” position
Connect the vehicle to the diagnostic tool
Start the engine
Select [Engine] from the menu
Select [Actual boost pressure] from the [Data monitor Setting] menu
Race the engine from idle to NMR and verify that the boost pressure output signal varies

STANDARD VALUES

There is no abnormal change in the sensor output signal.

(The pressure sensor signal response changes according to the engine speed)

Were there any abnormal changes in the sensor output signal?

Yes	Go to Step 4
No	Replace the boost pressure sensor. Clear all past DTCs. Check that no DTC is detected after test drive

Step 5: Inspect the intake air temperature sensor (intake manifold)

Check the installation of the intake air temperature sensor (intake manifold)
Make sure there is no dirt or damage to the intake air temperature sensor (intake manifold)

Were any failures found?

Yes

Clean the intake air temperature sensor (intake manifold) and install it properly. If damaged, replace the intake air temperature sensor (intake manifold).

Clear all past DTCs. Check that no DTC is detected after test drive.

Go to Step 8

Step 6: Inspect the intake air temperature sensor (intake manifold) unit

Set the starter switch to the “LOCK” position
Disconnect the intake air temperature sensor (intake manifold) connector
Use the electrical tester to measure the resistance between the terminals of the intake air temperature sensor (intake manifold)

MEASUREMENT CONDITIONS

TESTER CONNECTIONS

STANDARD VALUES

Starter switch: LOCK

Intake air temperature sensor

(intake manifold)

THG – E2

20°C {68°F}: 7.336 – 5.794 kΩ

50°C {122°F}: 2.435 – 1.994 kΩ

Do the measurements meet the standard value?

Yes

Go to Step 7

Replace the intake air temperature sensor (intake manifold)

Clear all past DTCs. Check that no DTC is detected after test drive.

Step 7: Inspect the response delay of the EGR valve [Diagnostic Tool]

Select [Inspection Menu] and then [EGR inspection] from the menu, then inspect the response delay at the Target EGR position and Actual EGR position

CAUTION: Perform the inspection while the engine is stopped to avoid damages

Inspection Procedure:

Select [Inspection Menu].
Select [EGR inspection].
Click [Start inspection].
Click [EGR opening UP]:

Inspect the response delay at each step of the Target EGR position and Actual EGR position from 0 to 100%.

Click [EGR opening DOWN]:

Inspect the response delay at each step of the Target EGR position and Actual EGR position from 100 to 0%

NOTE: The EGR opening position changes of around 10% per step between 0 – 10%

STANDARD VALUES

From the Target EGR position to the Actual EGR position, the response delay should be within 5 seconds

Do the measurements meet the standard value?

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

Step 8: Inspect the EGR cooler

Check if soot is obstructing the inlet/outlet of the EGR cooler gas passageway
Check if there are foreign substances stuck to the EGR cooler coolant passageway
Check the EGR cooler coolant passageway for obstruction due to deformation or other damage
Check if coolant is leaking from the EGR cooler

Were any failures found?

Yes	Remove the soot in the inlet/outlet of the gas passageway, or repair or replace the faulty part. Clear all past DTCs. Check that no DTC is detected after test drive.
No	Go to Step 9

Step 9: Inspect the EGR valve

Check the EGR valve for damage due to incursion of foreign substances.
Check if the inlet/outlet of the exhaust gas passageway is obstructed by soot

Were any failures found?

Yes	Remove foreign substances and clean the passageway. Replace the EGR valve if it is damaged. Clear all past DTCs. Check that no DTC is detected after test drive.
No	Go to Step 10

Step 10: Inspect the SCV

NOTE: For a detailed procedure, refer to the SCV Free Acceleration Test below

Were any failures found?

Yes	Repair or replace the faulty part.Clear all past DTCs. Check that no DTC is detected after test drive
No	Go to Step 11

Step 11: Inspect the injector [Diagnostic Tool]

Check the injection quantity and the rotational fluctuation

Start the engine
Select [Injection quantity] from [Data monitor Setting] on the diagnostic tool menu and measure the fuel injection quantity
Select [Engine speed] from [Data monitor Setting] on the diagnostic tool menu and measure the engine speed fluctuation

MEASUREMENT CONDITIONS

Engine speed: 1,500 r/min No-load, T/M shift lever: Neutral position, A/C off and Air compressor non-operating
Engine coolant temperature: more than 80°C {176°F}

STANDARD VALUES
TYPE OF	Q (mm³/st)	⊿Ne (r/min)
MT	5.0q ≤	≤ 26
Allison 2200	6.0q ≤
Allison 2500
Allison 3500

Do the measurements meet the standard values? (Are both injection quantity and engine speed fluctuation within the standard values)?

Yes	Go to Step 12
No	Replace the injector. Clear all past DTCs. Check that no DTC is detected after test drive

Step 12: Check the DTC detected (Engine ECU) [Diagnostic Tool]

Perform engine warm-up. (Engine coolant temperature: 60°C {140°F} or more)
Stop the engine
Set the starter switch to the “ON” position
Select [Engine] and check if P0401 has been detected

Has DTC P0401 been detected?

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

TEST METHOD

Engine Speed Pattern

After engine has reached operating temperature (more than 82ºC {179.6ºF})
After air compressor completed building pressure
A/C, Head lights off
All devices off. (PTO, Refrigeration compressor, etc.)
Control the engine revolution by means of operating Cruise Control system

Acceleration Pattern

After engine has reached operating temperature (more than 82ºC {179.6ºF})
After air compressor completed building pressure
A/C, Head lights off
All devices off. (PTO, Refrigeration compressor, etc.)
Check that actual common rail pressure following target

TYPES OF DATA TO BE MEASURED BY THE DIAGNOSTIC TOOL

Engine revolution
Engine coolant temperature
Injection quantity
Pump current target final value
Actual common rail pressure
Target common rail pressure

If the following symptoms occur, the test FAILS. If they do not occur, then test is OK

Pressure is reduced by 5 MPa or more continually for 5 seconds or more
Replace the supply pump

Pressure is increased by 5 MPa or more continually for 5 seconds or more.
Replace the SCV

The maximum common rail pressure exceeds 222 MPa for even a moment during pressure increase
Replace the SCV

After the maximum common rail pressure exceeds 222 MPa during pressure increase, the actual rail pressure falls below the target rail pressure.
Replace the SCV

Before the maximum common rail pressure exceeds 222 MPa during pressure increase, the actual rail pressure falls below the target rail pressure rapidly.
Replace the common rail.