Dtc P1251 Turbocharger / Supercharger Overboost Condition (Too High)

DESCRIPTION

WIRING DIAGRAM

INSPECTION PROCEDURE

CHECK FOR ANY OTHER DTCS OUTPUT (RECORD STORED DTC AND FREEZE FRAME DATA)

CHECK AIR INTAKE SYSTEM

REPAIR OR REPLACE AIR INTAKE SYSTEM

CHECK TURBOCHARGER SUB-ASSEMBLY (DC MOTOR OPERATION)

PERFORM ACTIVE TEST USING INTELLIGENT TESTER (ACTIVATE THE EGR VALVE CLOSE)

READ VALUE USING INTELLIGENT TESTER (TARGET EGR POSITION AND ACTUAL EGR VALVE POS.)

REMOVE DEPOSIT (ELECTRIC EGR CONTROL VALVE ASSEMBLY)

REPLACE EGR COOLER

READ VALUE USING INTELLIGENT TESTER (INJECTION VOLUME)

REPLACE INJECTOR ASSEMBLIES OF ALL CYLINDERS

BLEED AIR FROM FUEL SYSTEM

REGISTER INJECTOR COMPENSATION CODE AND PERFORM PILOT QUANTITY LEARNING

CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

CHECK HARNESS AND CONNECTOR (ECM - TURBOCHARGER SUB-ASSEMBLY)

DESCRIPTION

HINT:

Refer to DTC P0046 (HILUX_TGN26 RM000002PPL03VX_01.html).

HINT:

*: This value changes based on engine speed, atmospheric pressure and the engine coolant temperature (the value is generally between 119 and 279 kPa).

HINT:

If DTC P1251 is stored due to the VN turbo vane being stuck closed, the following symptoms may appear:

1. Vehicle surge when driving with full load
   
2. Sudden lack of power due to power being limited
   

WIRING DIAGRAM

INSPECTION PROCEDURE

NOTICE:

1. Inspect the fuses of circuits related to this system before performing the following inspection procedure.
   
2. After replacing the ECM, the new ECM needs registration (HILUX_TGN26 RM0000012XK058X.html) and initialization (HILUX_TGN26 RM000000TIN056X.html).
   
3. After replacing the fuel supply pump assembly, the ECM needs initialization (HILUX_TGN26 RM000000TIN056X.html).
   
4. After replacing an injector assembly, the ECM needs registration (HILUX_TGN26 RM0000012XK058X.html).
   

HINT:

Read freeze frame data using the intelligent tester. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, and other data from the time the malfunction occurred.

1. Connect the intelligent tester to the DLC3.
   

2. Turn the ignition switch to ON and turn the tester on.
   

3. Enter the following menus: Powertrain / Engine and ECT / DTC.
   

4. Read the DTCs.
   

   HINT:

   1. Record the stored DTCs and freeze frame data.
      
   2. Be sure to carefully examine "MAP" and "Target Booster Pressure" in the freeze frame data.
      

   Result

   Result	Proceed to
   P1251 is output	A
   P1251 and other DTCs are output	B

   HINT:

   DC motor-related DTCs: P0046, P0047 and P0048 (HILUX_TGN26 RM000002PPL03VX.html).

   Nozzle vane position sensor-related DTCs: P2564 and P2565 (HILUX_TGN26 RM000002PPN033X.html).

1. Check if the hoses between the air cleaner and turbocharger, and turbocharger and intake manifold are damaged or disconnected.
   
   

   Result

   Result	Proceed to
   Hoses or pipes are damaged or disconnected	A
   No hoses or pipes are damaged or disconnected	B

   HINT:

   1. Be sure to check if the hoses and pipes between the air cleaner and compressor are disconnected as disconnection of a hose or pipe can cause overboost. Also, check the high pressure hoses for disconnection due to overboost.
      
   2. Check for disconnection of the exhaust pipes.
      
   3. Using your hand, check whether the pipes and hoses in the intake system are securely connected.
      
   4. Check for any modifications in the intake system made by the user.
      

1. Repair or replace the malfunctioning part in the air intake system.
   

1. Check the turbocharger sub-assembly (HILUX_TGN26 RM000001A3W02JX_01_0010.html).
   

   HINT:

   Check the movement of the actuator rod when the ignition switch is turned from ON to off.

1. Connect the intelligent tester to the DLC3.
   

2. Start the engine and warm it up, and make sure the A/C switch and all accessory switches are off.
   

3. Turn the ignition switch off. Wait for 30 seconds, and then restart the engine.
   

4. Turn the tester on.
   

5. Enter the following menus: Powertrain / Engine and ECT / Data List / MAF.
   

6. Read the MAF value displayed on the tester while the engine is idling.
   

7. Enter the following menus: Powertrain / Engine and ECT / Active Test / Activate the EGR Valve Close.
   

8. Read the MAF value when the EGR valve is closed using the Active Test function.
   

   HINT:

   1. If idling continues for 20 minutes or more, the EGR valve target opening angle becomes 0% (EGR valve fully closed). As this makes diagnosis impossible, it becomes necessary to drive the vehicle or to restart the engine.
      
   2. Before performing the diagnosis, confirm that the EGR valve target opening angle is not 0%.
      
   3. When "Coolant Temp" is 75°C (167°F) or higher during idling, the exhaust gas flows through the EGR cooler. If MAF does not change when the EGR is cut even though the EGR valve is operating normally, the EGR cooler may be clogged.
      
   4. When idling while warming up the engine, the actuator operates and the EGR cooler is bypassed. However, if the connector of the VSV for the EGR cooler is disconnected, the EGR cooler is not bypassed and it is possible to check how clogged the EGR cooler is.
      
   
   

   Result

   Active Test	Result	Proceed to
   Activate the EGR Valve Close: Off (Open) to On (Closed)	MAF value does not change	A
   	MAF value changes	B

   NOTICE:

   As the measured values may differ from those shown below due to factors such as differences in measuring environments and changes in vehicle condition due to aging, do not use these values to determine whether the vehicle is malfunctioning or not.

   HINT:

   The problem may be a temporary one, due to the entry of deposits or foreign matter. Check that there are no deposits or foreign matter in the electric EGR control valve assembly or mass air flow meter.

   
   

   Reference:

   
   

   EGR Valve Condition (Opening)	Measuring Condition	MAF (Reference)
   Open (55%)	Atmosphere pressure: 101 kPa Intake air temperature: 30°C (86°F) Engine coolant temperature: 88°C (190°F)	3 to 10 gm/s
   Closed (0%)		12 to 21 gm/s

1. Check the change in the values of "Target EGR Position" and "Actual EGR Valve Pos." in the Data List from the time when the "Control the EGR Step Position" or "Activate the EGR valve Close" Active Test was performed in the previous step.
   
   

   Result

   Result	Proceed to
   Even though "Target EGR Position" indicated that the system was commanding the valve to open, "Actual EGR Valve Pos." remained near 0% and did not change	A
   Other than above ("Actual EGR Valve Pos." changed according to the EGR valve open/close commands of the Active Test)	B

1. Remove the electric EGR control valve assembly (HILUX_TGN26 RM000004QWK009X.html).
   

2. Visually check the electric EGR control valve assembly for deposits. If there are deposits, clean the electric EGR control valve assembly.
   

   HINT:

   1. If the EGR valve is stuck closed, the intake air amount increases and engine vibration may worsen.
      
   2. If the EGR valve does not close properly or is stuck open, EGR becomes excessive and combustion becomes unstable. Also, there may be a lack of power.
      

3. Reinstall the electric EGR control valve assembly (HILUX_TGN26 RM000004QWK009X.html).
   

1. Replace the EGR cooler (HILUX_TGN26 RM000004QWO009X.html).
   

1. Connect the intelligent tester to the DLC3.
   

2. Start the engine and warm it up until the engine coolant temperature reaches 70°C (158°F) or higher.
   

3. Allow the engine to idle for 1 minute or more.
   

   HINT:

   The A/C switch and all accessory switches should be off with a fully warm engine.

4. Turn the tester on.
   

5. Enter the following menus: Powertrain / Engine and ECT / Data List / Injection Volume.
   

6. Read the values during engine idling.
   
   

   Result

   Result	Proceed to
   Injection Volume is less than 5 mm3/st	A
   Except above	B

   HINT:

   1. If the injector assembly is malfunctioning, the compensatory injection volume remains at 5.0 mm³/st.
      
   2. If there is a disconnection, the feedback value will increase and +5.0 mm³/st will be indicated, because it will become impossible for the injector to inject.
      

1. Replace the injector assemblies (HILUX_TGN26 RM0000044TN00FX.html).
   

   NOTICE:

   1. When replacing the injector assembly for a cylinder, always be sure to use a new injection pipe.
      
   2. Follow the procedure in the repair manual and temporarily install the injection pipes and nozzle leakage pipe, and then correctly position the injector assemblies. After that, tighten parts according to the torque specifications.
      
   3. If the installation procedure is not performed correctly, injector assemblies may become out of position, which may cause the injector assemblies to deteriorate, resulting in malfunctions.
      
   4. If an injector assembly deteriorates and malfunctions, other problems such as knocking, rough idle, etc. may occur.
      
   5. If an injector assembly becomes out of position, it is possible that the seal between the injector assembly and injection pipe may become incomplete, resulting in a fuel leak.
      

1. Bleed the air from the fuel system (HILUX_TGN26 RM000002SY802GX_01_0002.html).
   

1. Register the injector compensation code (HILUX_TGN26 RM0000012XK058X_02_0003.html).
   

2. Perform the injector pilot quantity learning (HILUX_TGN26 RM0000012XK058X_02_0009.html).
   

1. Connect the intelligent tester to the DLC3.
   

2. Clear the DTCs (HILUX_TGN26 RM000000PDK0X2X.html).
   

3. Turn the ignition switch off.
   

4. Start the engine and warm it up.
   

5. Confirm the value of Engine Speed from the Freeze Frame Data recorded previously, and then drive the vehicle according to the Engine Speed value.
   

   HINT:

   Take a snapshot of "MAP" and "Target Boost Pressure" in the Data List with the intelligent tester while driving the vehicle.

6. Read the DTCs.
   
   

   Result

   Result	Proceed to
   P1251 is not output and the amount by which MAP exceeds Target Boost Pressure is 20 kPa or less	A
   Except above	B*

   HINT:

   *: Return to "Check Air Intake System" and inspect areas that have not been inspected yet.

1. Disconnect the DC motor connector.
   

2. Disconnect the nozzle vane position sensor connector.
   

3. Disconnect the ECM connector.
   

4. Measure the resistance according to the value(s) in the table below.
   
   

   Standard Resistance:

   
   

   Tester Connection	Condition	Specified Condition
   C41-1 (M-) - C112-14 (M-)	Always	Below 1 Ω
   C41-2 (M+) - C112-15 (M+)	Always	Below 1 Ω
   C40-1 (VTA1) - C114-6 (VNA)	Always	Below 1 Ω
   C40-2 (VNE2) - C114-10 (VNE2)	Always	Below 1 Ω
   C40-3 (VNVC) - C114-11 (VNVC)	Always	Below 1 Ω
   C41-1 (M-) or C112-14 (M-) - Body ground	Always	10 kΩ or higher
   C41-2 (M+) or C112-15 (M+) - Body ground	Always	10 kΩ or higher
   C40-1 (VTA1) or C114-6 (VNA) - Body ground	Always	10 kΩ or higher
   C40-3 (VNVC) or C114-11 (VNVC) - Body ground	Always	10 kΩ or higher

5. Reconnect the DC motor connector.
   

6. Reconnect the nozzle vane position sensor connector.
   

7. Reconnect the ECM connector.