Hino P0234 Fault Code: Overboots

Technical Description

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

Description Of Malfunction

Boost pressure is higher than the stipulated value

DTC Set Condition

DTC Detection Condition:

At all times when engine is running (Detectable 10 minutes after engine start-up)

Judgment Criteria:

• Boost pressure value above threshold value is detected (abnormally high)
• Deviation between target boost pressure and actual boost pressure: 37 – 45 kPa {5.4 – 6.5 psi}

Reset Condition

After normal operation is restored and the starter switch is on the “LOCK” position

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
• Insufficient output or engine stall because of DPR filter clogging due to abnormal soot generation

Pre-Inspection Work

Check that the battery voltage is in the normal range

After-Inspection Work

• Clear all past DTCs
• Check if the DTC is stored after test drive

Possible Causes

• VNT actuator failure (VNT nozzle closed-side failure)
• EGR valve failure (EGR valve closed-side failure)
• Clogged boost pressure sensor hose
• Boost pressure sensor failure (abnormal voltage, power supply or ground fault)

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 P0234 (for example, P0045, P0401) has been detected

Has a DTC other than P0234 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]

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 and select [Engine]
4. 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%

1. 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 responsedelay 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%

1. 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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