Your Master May Hide All These Maintenance Experience 3 types
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The Symptom And Troubleshooting Method Of Automobile Drive Shaft Broken
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Your Master May Hide All These Maintenance Experience From You

As long as we mention the common rail system, we will think of Bosch, electric equipment, Delphi and Cummins; However, each manufacturer’s definition and design of common rail system are different, which will lead to deviation in fault judgment and even failure point maintenance experience. This issue of small rail will bring you a failure case of electrical installation.

Case sharing of maintenance experience

Maintenance experience steps are as follows:
maintenance experience of1. Use a diagnostic expert to read the fault code

  • Use the decoder to read three current fault codes:
  • P2122 — the voltage of acceleration sensor circuit 1 is too low;
    P2127 – the voltage of acceleration sensor circuit 2 is too low;
    P2120 – acceleration sensors 1 and 2 fail;
  • Judging from this fault code, the accelerator sensor is faulty, and check the accelerator sensor and related harness.

maintenance experience of 2. Check the harness voltage of accelerator sensor

  • The measured values of 5V, 0V and 0V are normal; Measure the connection and disconnection of the six harnesses. The connection and disconnection of the harness are normal, and the signal wire is not short circuited to the ground. It is suspected that there is a problem with the accelerator pedal.

maintenance experience of 3. Replace the accelerator pedal

  • After replacing the sensor, use the decoder to read the fault code, and the system display is normal.

maintenance experience of 4. Test run

  • Let the master test drive and find that it is still idle jitter and can’t add oil. Read the data stream
  • From the data flow, it can be preliminarily determined that there is no problem with the intake pressure, the cooling water temperature and fuel temperature, and the accelerator pedal sensor data. However, there is a deviation between the PCV closing timing 120ca and the normal value, which is between 135-145ca. It is suspected that there is a problem in the fuel circuit.
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  • Tips
    In the data stream, we can see that the voltage of accelerator pedal 1 is not twice the voltage of accelerator pedal 2, but there is no error; This is because the detection of some electrically installed accelerator pedal sensors adopts a 1:1 redundant design, which is different from the 1:2 design seen by most of us.

maintenance experience of 5. Oil circuit inspection

  •  Connect the low-pressure pipeline directly, and the fault remains. Eliminate the problem of low-pressure pipeline;
  •  Check the overflow valve on the fuel filter and the overflow valve of the high-pressure oil pump and find that they are not stuck.
  •  Disconnect the PCV1 circuit so that no high-pressure oil from PCV1 is input into the high-pressure common rail pipe. The starting engine can start normally, and it is preliminarily determined that there is no problem with PCV2 and the corresponding plunger.
  •  Disconnect the PCV2 circuit so that no high-pressure oil from PCV2 is input into the high-pressure common rail pipe. If the starting engine cannot start normally, it can be determined that there may be a problem with PCV1 valve and corresponding plunger
  • Tips
    For normal hp0 pump, two high-pressure plungers supply oil to the common rail pipe. When one of them stops supplying oil, the engine can start normally; In step 5, disconnect the PCV2 circuit and use a plunger to supply oil. If the engine cannot start, there is a problem with the oil supply in this circuit. Check the PCV1 valve and high-pressure plunger.

maintenance experience of 6. Replace the PCV valve

  • After replacement, the fault is removed and the problem point is found。

Fault postscript

  • After a month of maintenance, the car has the same fault phenomenon again. It vibrates at idle speed and can’t add oil, but there is no fault code. Use the decoder to read the data stream.


  • The above fault phenomenon is very common in the electric installation system (Shangchai electric installation, Xichai electric installation and Hino electric installation). The small rail encounters many faults with no fault code, insufficient power and sometimes speed limit of 1500 rpm, which are all the problems of rail pressure sensor.
  • At the same time, when the deviation between the target rail pressure and the actual rail pressure exceeds 100bar, the electrical installation system will report a fault, while the Bosch system is generally calibrated to 200bar.

Case sharing of maintenance experience

  • I believe you have no problem with the previous troubleshooting, but you will still have doubts about the “fault postscript”. Why did you not report the fault code when it was clearly the fault of the rail pressure sensor? If it is other systems, will this phenomenon also occur?
  • To explain this problem, we need to talk about the fault logic of different systems.

Knowledge expansion

  • The principle of common rail system of different manufacturers is generally the same, but there are still differences in some details. Let’s talk about the fuel injection control of electric equipment.
  • The control determines the fuel injection amount by adding coolant temperature, fuel temperature, intake temperature and intake pressure correction to the basic injection amount. The engine controller calculates the basic injection amount according to the engine working conditions and driving conditions.

a. Calculation method of injection quantity
The calculation includes comparing the following two values:

  •  Basic injection quantity calculated from accelerator position and engine speed in governor mode.
  • The injection quantity obtained from the engine speed by adding different types of corrections to the maximum injection quantity. The smaller of the two injection quantities is used as the base for calculating the final injection quantity.
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b . Set injection quantity

  • Basic injection quantity
    This quantity is determined by engine speed and accelerator pedal opening. When the engine speed is constant, if the opening of the accelerator pedal increases, the injection volume increases; When the accelerator pedal opening is constant, if the engine speed increases, the injection amount
  • Starting injection volume
    This quantity is determined according to the basic injection quantity when the engine is started and the correction for the on time of starter switch, engine speed and coolant temperature increase. If the coolant temperature is low, the injection volume increases. This mode is cancelled when the engine is fully started. 
  • Maximum speed set injection volume
    Determined by engine speed. Limit the amount of injection in order to prevent excessive increase in engine speed (overspeed).
  •  Maximum injection volume
    This is determined by the engine speed and the basic maximum injection quantity determined for the correction of the increase of coolant temperature, fuel temperature, intake air temperature, atmospheric temperature, intake air pressure, atmospheric pressure and full Q adjustment resistance (only for the first generation hp0 system).

c. Correction

  • Engine maximum injection correction (when the engine is warm)
    When the coolant temperature is low, this correction will increase the injection amount whether during start-up or normal operation.
  •  Intake pressure correction
    When the intake pressure is low, the maximum smoke emission is reduced.
  •  atmospheric pressure correction
    The maximum injection volume increases and decreases according to the atmospheric pressure. When the atmospheric pressure is high, the maximum injection volume increases.
  •  Delay correction for accelerating injection quantity
    When accelerating, if the opening of the accelerator pedal changes greatly, the injection amount will be delayed to increase in order to prevent black smoke emission.
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