Symptom:
    A 2009 FAW - Volkswagen Magotan 1.8TSI sedan, according to the user to reflect the car in the acceleration of the poor, the instrument on the EPC lights lit alarm.
    Failure analysis:
    Use the fault diagnosis instrument VAS5051 to detect the engine control unit stored in the fault code 08852 (fuel pressure regulator N276 open circuit), the fault code for a permanent failure, can not be cleared. Read the data stream 01-08-140 group 3, shows the fuel pressure at idle speed of 700kPa, and the standard value should be about 4MPa, the test results show that the fuel system can not establish high pressure.
    The Volkswagen PQ46 platform is equipped with an electronically controlled direct injection engine, and the fuel high pressure is regulated by a pressure regulator N276 mounted on a fuel pump. During the injection process, the engine control unit sends a command to the fuel pressure control valve N276 according to the calculated fuel supply start point, so that the needle valve moves forward against the force of the needle valve spring, and the oil inlet valve is moved in the spring force Under being closed. As the pump piston moves upwards, the oil pressure is established in the pump chamber. When the oil pressure in the pump chamber is higher than the oil pressure in the oil rail, the oil valve is forced to open and the fuel is pumped into the oil rail. In the oil rail to form a stable high-pressure fuel pressure by the pressure sensor to identify and send the signal to the engine control unit, by reading the data stream 01-08-140 group 3 show the pressure we can analyze whether the normal establishment of high pressure.
    Based on the above analysis of the high pressure of the fuel, the possible reasons for the high pressure of the fuel supply system can not be established include: damage to the camshaft drive, high pressure regulator pump failure, high voltage regulator pump control line fault and engine control unit failure. But the combination of fault code on the pressure regulating valve N276 open circuit tips, it is necessary first through the VAS5051 implementation of the self-diagnostic function of the fuel pressure regulator N276 line test, found that the implementation of self-diagnosis when the N276 touch the shell without any reaction, The VAS5051's self-diagnostic interface display system is activated and the loop is closed, since the "click" sound is controlled by the engine control unit at a certain frequency. So the initial judgment of the engine control unit there is little chance of control failure, the fault point should be locked in the implementation of N276 line.
    According to the regulator N276 control circuit, the regulator N276 has two terminals. T2gz / 1 terminal via SB17 fuse connected to engine high pressure pump control relay J49 87 feet for the supply of power from the main relay; T2gz / 2 terminal to the engine control unit T60ya / 19 terminal, used to accept the control unit of the work control signal. The N276's T2gz / 2 terminal is connected to the T60ya / 19 terminal of the engine control unit. The N276's T2gz / 1 terminal is connected to the engine high-pressure pump control relay. The N276's T2gz / 2 terminal is connected to the T60ya / 19 terminal of the engine control unit. J49 87 feet between the terminals of the circuit breaker; J49 relay circuit itself; J49 external power supply line open.
    Unplug the harness connector of N276 and use T2gz / 1 as the measuring point to detect that the control waveform of the engine is the normal negative trigger waveform in the ignition state, which means that the T2gz / 2 terminal of N276 is connected to the T60ya / 19 terminal of the engine control unit Road breaking phenomenon. To N276 T2gz / 1 terminal as the measurement point, to detect the ignition state without the supply voltage, which can be inferred N276 power supply circuit circuit failure. Measure the high voltage pump control relay J49 87 feet to N276 T2gz / 2 feet line normal, which can determine the fault is the relay J49 internal or external power supply reasons. To relay J49 as the test center, measuring its 30 terminal has a normal power supply voltage, 85 feet from the main relay SB23 control, measured its normal 15 power supply. Further measurement of the J49 relay control coil resistance (85 feet and 86 feet) is 82Ω, compared to the standard resistance is normal, the initial test components are normal, but the power cord is powered low. In order to track this problem, open the relay shell, observe the ignition gear when the relay side of the implementation of the two contacts do not pull, indicating that the relay control coil in the internal operation of the virtual connection can not provide the required circuit Closing force.
    Replace the J49 relay, fault code 08852 can be cleared. At this point the use of VAS5051 test function, enter the engine system N276 implementation of component self-diagnosis, you can hear the N276 in accordance with a certain frequency of the "click" sound, indicating the engine control unit to high pressure regulator pump control back to normal, this time Read the idle when the 140 group shows the fuel working pressure of 4MPa, thus the fault completely resolved.
    Maintenance summary:
    It should be noted that, for the MAGOTAN sedan, the fuel can not be established high pressure failure is basically caused by high pressure regulator internal mechanical failure, the pump is usually jammed at the bottom dead point, can not be camshaft through the cylindrical tappet The effective stroke of the drive, which can not establish the corresponding direct injection of oil pressure. Engine control unit to monitor the work of the hydraulic range of ultra-poor, and then integrated high-voltage regulator without electric control circuit fault code identification logic analysis, so there will be fault code 08851 (fuel pressure regulator N276 mechanical failure) fault code storage The In this case, because the relevant control circuit is broken, resulting in the fault code 08852 storage, which can be seen the same phenomenon but the fault is very different, which prompted us to check the electronic control failure, we must follow the diagnostic testing process for a comprehensive analysis , Targeted to solve the problem, in order to avoid the misunderstanding of empiricism.