Passat
The vehicle is driven with a weak pickup and a lack of power, and the malfunction light is illuminated. Let’s see what exactly causes this.
Troubleshooting
Connect diagnostics and test engine fault store: P0234 Boost pressure control: beyond control limit.
After clearing the faulty test car, as long as the rapid accelerator, the first-foot strong power, and then step on the gas pedal power becomes very poor, and cannot pick up speed. Through the relevant understanding of this vehicle because the original engine due to vehicle accidents damaged, to replace the engine assembly.
Fault analysis
Since the engine assembly has been replaced, mechanical engine failure has been largely ruled out. The engine computer board reports that the boost system pressure is too high, exceeding the control limits; and there is no reported malfunction of the boost pressure limiting solenoid valve N75 or G31, but the system reports that the supercharger is over-boosted, and the possible causes of the malfunction are.
- pressure detection circuit G31 failure
- N75 control and management failure
- supercharger pressure tank adjustment failure.
According to the analysis, the maintenance personnel decided to check around the boost pressure detection and N75 control, according to the data group 114, 115 group response pressure, data boost air valve duty cycle data, and data at idle.
At idle, the graph shows that the actual value of the idle boost pressure, 990 mbar, is greater than the boost target value of 420 mbar.
During rapid acceleration, the pressurized data flow.
The graph shows that during rapid acceleration, the actual boost value of 1930 mbar is also greater than the target boost value of 1100 mbar.
Comparison of the above data can be clearly seen, observe the high load data flow, channel number under the third item of the theoretical increase in boost pressure data, as well as the fourth item below for the actual boost pressure data. Derived G31, the engine on the N75 control is normal but observed that the faulty car’s high load of the actual boost pressure data is significantly larger than the standard boost pressure data value, which shows the vehicle failure for the over-boosting. Enough to rule out G31/engine/N75 control line failure, the failure may be in the N75 pressure control and turbocharging pressure tank adjustment.
N75 is controlled by duty cycle, through the engine control unit to control different duty cycle signals to realize N75 detection and make turbocharger pressure tank to get to make the turbo boost, hold pressure, buck control pressure. The Turbocharger pressure tank is controlled by adjusting the bolt control bypass valve opening to reduce the exhaust gas turbine flow to control the pressure. The cooperation between the two to achieve the purpose of controlling the normal operation of the engine boost pressure.
The next analysis revealed the following status for the N75.
- Total speed 2% duty cycle when the supercharger pressure tank is under pressure, G31 detects pressure low pressure.
- High speed boosts 96% duty cycle when the supercharger pressure tank is in a vacuum state, G31 detection pressure high pressure.
- N75 according to the engine monitoring G31 signal, output duty cycle signal to control, N75 according to the instruction modulation out of the turbocharger pressure tank pressure signal to make the pressure control in 300-700 bar. so as to ensure that the engine is at normal working pressure.
Fault resolution
To figure out the principle, maintenance personnel have checked the N75-related piping without shedding leakage phenomenon. Try to N75 turbocharging pressure chamber and turbocharging pressure tank piping directly connected, the control system no longer reports faults, and the pressure data shows that the engine is in a non-boosted state.
At this time, the fault is locked in the N75 boost regulator solenoid valve. After replacing the N75 solenoid valve, and repeated test drives, the vehicle power is abundant, with excellent acceleration performance. Original vehicle troubleshooting.
Case summaries
The troubleshooting of this faulty car gave us a deeper understanding when repairing turbocharging faults. That is when observing the boost data, more attention should be paid to observing the acceleration (when the load is large) of the boost pressure requirements and the actual boost pressure comparison because when idling, the turbo is not involved in the work. At the same time, we should pay more attention to the pre-installation inspection of engine accessories in the future, if this faulty solenoid valve is also checked for ventilation performance before installation, it may not lead to the later diagnosis of this fault.
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