20 18 Volkswagen C-TREK accelerated fault diagnosis and maintenance case.

Author: Zhao Yubin, the treasure of Sino-Singapore Hebidian has faults. 20 18 Volkswagen leads the way, equipped with EA2 1 1 engine, with a cumulative mileage of about 40,000 km. The owner said that the engine failure indicator light was on when the vehicle was driving, and there was no acceleration. After fault diagnosis and debugging after receiving the car, the fault phenomenon reflected by the owner is true. According to the detection result of the fault detector, the fault code "P029900 Turbocharging Control-Active/Static Control Limit Not Reached" is stored in the engine control unit (J623) (Figure 1). According to the fault code, it is suspected that the intake pressurization is low. The fault code (screenshot) read in Figure 1 is tested after clearing the fault code. When the vehicle suddenly accelerates, the acceleration is slow. Reading the pressurized data stream, the actual pressurization is about1.2 bar (1bar =100 kpa), which is quite different from the standard pressurization 1.8bar, and the fault code is consistent with the data stream. J623 obtains the boost information through the boost sensor (G3 1) installed in front of the throttle. The cause of the failure is divided into the following two parts. ) 1) The actual pressurization pressure of the pressurization pipeline is sufficient, but the data detected by J623 is wrong. ) The actual pressurization on the pressurization pipeline is really too low. Using the waveform function of the fault detector to read the waveform of the boost signal and the waveform of the intake manifold absolute pressure signal (measured by the intake manifold absolute pressure sensor and installed behind the throttle), it is found that the change trend of the two waveforms is almost the same when the accelerator pedal is suddenly stepped on. In the analysis of the signal voltage waveform (screenshot) read in Figure 2, it is considered that the possibility of signal distortion caused by two sensors at the same time is extremely low, and the failure possibility of J623 is also low. Since the first possibility mentioned above is temporarily ruled out, it is inferred that the absolute pressure signal waveforms of the intake manifold are basically the same. According to the data, the intake pressurization of the turbocharger system of this vehicle is controlled by the pressurization limiting solenoid valve (N75, installed on the turbocharger), and the adjustment of the air circulation pressure reducing valve (N249) is cancelled. When the engine is in a low-speed and low-load state, N75 is normally closed, connecting the wastegate actuator pipeline and the pressurized high-pressure air pipeline. When the boost pressure increases, the pressure acting on the wastegate actuator also increases, which increases the opening of the wastegate valve. Therefore, when the engine is accelerating or in a high-speed and high-load state, J623 controls the switching signal of N75 with the duty ratio. When the N75 braking signal is received, the inner valve body is displaced, the pipeline of the wastegate actuator is connected with the low-pressure air pipeline before pressurization, the force on the wastegate actuator is reduced, the wastegate valve is closed, and the exhaust pressure of the turbocharger is increased. This paper analyzes the possible fault causes of insufficient intake pressurization, the faults of turbocharger and exhaust pipe. N75 fault; N75 pipeline connection error. Check the connection of N75 pipeline, and no abnormality is found. N75 is a normally closed solenoid valve. In case of power failure, the actuator pipeline of the wastegate valve is communicated with the pressurized high-pressure air pipeline. When the actuator of the wastegate is pressurized, the bypass valve is opened and the pressurization pressure is reduced. The turbocharger and the wastegate cut off the pipeline connection between N75 and the wastegate actuator (the wastegate valve is always closed), connected to the fault detector for path test, and read the engine data stream, and found that the intake boost pressure obviously increased to about 3bar. Figure J623 Engine data flow (screenshot) According to Figure 4, the power waveform (red), control signal waveform (blue) and working current waveform (yellow) of N75 are measured by microcomputer, and the signal voltage waveform (green) of G3 1 is also measured. Fig. 4 (fig. 5) shows waveforms measured by circuit analysis N75 and G3 1. A current in the line indicates that the coil circuit of N75 is turned on, and the signal voltage output by G3 1 also rises slowly under the control of J623. Everything looks normal, but if you think back carefully about the action current waveform of the injector, there will be an inflection point in the process of the action current rising. In other words, the current continues to increase after decreasing. The reason of inflection point is that when the solenoid valve is opened, it will produce induced voltage, which will reduce the working current. It can be inferred that N75 did not work normally when it got the braking signal. Figure 5 Fault waveform (screenshot) N75 Remove and power on test. The valve body moved slightly, and all three pipelines on N75 were connected after being electrified, which was abnormal. As shown in fig. 6, usually when N75 is energized, pipeline A communicates with pipeline C; Connect pipe a and pipe b after electrifying. At this point, N75 has been confirmed damaged. Fig. 6 Fault diagnosis of damaged N75 After N75 was replaced, it was put into trial operation and the vehicle accelerated normally. The measured waveform is shown in Figure 7, and the working current waveform of N75 has an inflection point with the open circuit of the slide valve. Fig. 7 Summary of normal waveform fault (screenshot) Due to the internal damage of N75, the solenoid valve coil can be normally energized, but the valve column only slightly displaced when it was sucked in, and the low-pressure air pipeline was not completely opened before pressurization. When the actuator pipeline of the wastegate valve and the pressurization pipeline N75 are energized, the three pipelines are communicated. When pressurization is required, the wastegate valve is always pushed open and cannot be closed. Pixar lens with rising boost pressure keenly captures the induced voltage signal.