Hino P0299 Fault Code: Underboost

Technical Description

The VNT moves the nozzle vane stepless by the REA (Rotary Electric Actuator) to control the turbo speed and boost pressure. It compares the target boost pressure and actual boost pressure to check if the actual pressure is lower than the target pressure.

Description Of Malfunction

The boost pressure is lower than the stipulated value

DTC Set Condition

DTC Detection Condition:

While the engine is in operation – Always. (Detection is available after 10 minutes of engine start)..

Judgment Criteria:

Compare the target boost pressure and actual boost pressure: (45 – 65 kPa {6.5 – 9.4 psi}).

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

Symptoms On The Vehicle When The DTC Is Set

Symptoms on the Vehicle Due to Malfunction:

− Engine lack of power due to lack of air intake volume.

− Turbocharger abnormal noise/damage.

− Lack of power or engine stall due to DPR filter clogged (excessive soot generation).

Pre-Inspection Work

Check that the battery voltage is in the normal range.

After-Inspection Work

− Clear all past DTCs.

− Check if no DTC is stored after test drive.

Possible Causes

− Abnormality in air intake system (disconnected boost hose).

− Turbocharger failure (stuck turbine).

− Malfunction of boost pressure sensor.

− Malfunction of air flow sensor.

− Malfunction of VNT.

− Malfunction of EGR valve.

Inspection Procedure

Troubleshooting Steps

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

1. Set the starter switch to the “LOCK” position.
2. Connect the vehicle to the diagnostic tool.
3. Set the starter switch to the “ON” position.
4. Select [Engine] and check if any DTC other than P0299 (for example, P0045, P0401) has been detected.

Has a DTC other than P0299 been detected?

Step 2) Inspect the boost pressure sensor hose.

1. Make sure the boost pressure sensor hose is not clogged, ruptured, or cracked.
2. Make sure the pipe on the intake manifold side is not clogged.

Were any failures found?

Step 3) Inspect the boost pressure sensor power supply system.

1. Set the starter switch to the “LOCK” position.
2. Disconnect the boost pressure sensor connector.
3. Set the starter switch to the “ON” position.
4. Use the electrical tester to measure the voltage between the terminals of the boost pressure sensor vehicle-side connector.

Do the measurements meet the standard value?

Step 4) Inspect the response delay of the VNT controller [Diagnostic Tool].

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

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

Inspection Procedure:

1. Select [Inspection Menu].
2. Select [VNT inspection].
3. Click [Start inspection].
4. Select [VNT UP]:

− Inspect the response delay at each step of the Target VNT position and Actual VNT position from 0 to 90%.

5. Select [VNT DOWN]:

− Inspect the response delay at each step of the Target VNT position and Actual VNT position from 90 to 0%.

NOTE: The VNT opening position changes of around 10% per step between 0 – 90%.

Do the measurements meet the standard value ?

Step 5) 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:

1. Select [Inspection Menu].
2. Select [EGR inspection].
3. Click [Start inspection].
4. Click [EGR opening UP]:

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

5. 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 – 100%.

Do the measurements meet the standard value?

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