2012 Volkswagen Myrtle Performance Fuel Pump Circuit Troubleshooting Case Study

Date: 2020-12-16        Clicks: 1326



The role of the performance fuel pump circuit is: when the ignition switch is switched on, the performance fuel pump is controlled to work for about 3s to establish the pre-oil pressure so that when the vehicle is started, it can be started smoothly, if there is no pre-oil pressure in the fuel supply rack when starting, it will lead to long starting time of the vehicle. During and after the vehicle starts, the performance fuel pump circuit can control the performance fuel pump to work to provide a stable oil pressure to the supply rack, and then control the fuel injection volume by controlling the injector fuel injection time, so as to achieve precise control of the air-fuel ratio. At present, the performance fuel pump control circuits of various models differ in structure, and the circuit working principles and control methods are also very different. 


If a simple control circuit is encountered, most of them are performance fuel pump fuse, performance fuel pump relay or performance fuel pump failure, which can be eliminated by using the replacement method during maintenance. Therefore, for complex circuits, it is necessary to read and understand the working principle of the circuit, analyse the cause of the fault, then form a fault diagnosis plan, and then implement the fault diagnosis according to the fault diagnosis plan.




2 2012 Volkswagen Myrtle performance fuel pump circuit composition and working principle analysis


2.1 Composition of the performance fuel pump circuit


It is mainly composed of low pressure performance fuel pump G6, performance fuel pump control unit J538, performance fuel pump fuse SC36, on-board grid control unit J519 and engine control unit J623 and other components.


2.2 performance fuel pump circuit working principle


When the ignition switch is switched on, the ignition switch provides a 15 signal to J519. After receiving the 15 signal, J519 outputs a wake-up signal to terminal J538T10p/7. After receiving this signal, J538 controls the low pressure performance fuel pump G6 to run at high speed for about 3s to establish the pre-oil pressure. After the engine is started, the engine control module J623 outputs PW M pulses to terminal JS38T10p2 through terminal T94/30 according to the signals detected by the sensors (engine load, speed, etc.), and J538 outputs variable voltage to the performance fuel pump after signal processing. The higher the engine load, the wider the PWM pulse width output by J623 and the higher the performance fuel pump running speed, thus achieving automatic


The higher the engine load, the wider the PWM pulse width of J623 output, the higher the performance fuel pump operation speed, thus achieving the role of automatic fuel pressure adjustment, achieving the purpose of fuel saving at low speed and making the engine powerful at high speed.




3 Fault diagnosis case analysis


3.1 Fault phenomenon


A 2012 Volkswagen Myrtle car, start normally, the engine can start, but after 30-40s after starting, soon stalled, when stepping on the accelerator pedal, stalled even faster, at the same time the instrument panel engine fault indicator light is always on.


3.2: Preliminary judgment


The preliminary judgment is that the performance fuel pump circuit PWM signal is faulty.


3.3 Failure Cause Analysis


3.4 Troubleshooting procedure


1) Confirm the fault phenomenon, turn on the ignition switch, start the vehicle, the engine starts normally, after starting 30-40s soon after stalling, observe the instrument display, find the instrument panel engine fault indicator light, read the fault code with decoder, the fault code shows 00602; "performance fuel pump module actuation, electrical fault disconnection", carry out the next check.


2) Turn on the ignition switch, enter the 106 channel to read whether the oil pressure data stream is normal, the fuel rail pressure shows 36.91 bar, start the vehicle, monitor the system oil pressure, found that the oil pressure continues to drop, when the fuel pressure drops to 1.88 bar, the engine stalls, monitoring results as shown in Figure 4, indicating that the performance fuel pump does not work after starting, carry out the next test.


3) After starting the vehicle, immediately test the J538T10P/2 terminal PWM pulse signal with an oscilloscope to see if it is normal, the result shows no PWM pulse waveform, then monitor the J623T94/30 waveform with an oscilloscope, the waveform is normal, indicating that there is a fault in the communication line between J538 and J623, and then repair the communication line.


4) After repairing the line, start the vehicle, the vehicle runs normally, the engine fault indicator is off, the fault is eliminated. The liquid level is normal, and the feedback voltage of the liquid level sensor is abnormal, so lock the fault for the liquid level sensor damage.


3.5 Troubleshooting


Replace the new coolant level sensor, start the engine, the yellow engine fault light immediately disappears, clear the fault code, the fault is eliminated.


4 fault summary


After encountering the fault, the first thing to do is to clarify whether the current fault is reproduced, and what are the conditions under which the fault occurs, such as how much engine speed, how much water temperature and other conditions before the fault. Then according to their own maintenance experience, knowledge base, a variety of technical information and maintenance manuals, etc. to analyze the possible causes of the fault, you can certainly find the fault point.




This article is quoted from Technical Communication Using the Repair