In our school, Inzorcaricar Diagnosities, we always teach students not to trust error codes that appeared in the system, but to carry out a full analysis of the car malfunctions. After all, the error code may not be the cause, but a consequence of another fault. Judge for yourself.
The owner of Mercedes-Benz ML W166 with a diesel engine turned to us. In the car service where the car used to be serviced, because of a decent run (more than 150 thousand km), it was washed with a fuel system (TC) on a special installation. And after the procedure, the Check Engine indicator on the dashboard was caught fire.
There were no problems other than the increased fuel consumption of the car. The owner also felt that the dynamics of the car was slightly worse with the advent of the burning signal on the panel. The service was offered to adapt, but could not do that. Well, and recommended replacing the pressure control valve on the TNVD or the TNVD itself assembly.
After all the peripetia, the car was with us.
We conducted an engine error codes and found an active malfunction code — P11BF00 «High pressure valve control range in a closed state.»
Next, we checked the current parameters using the AutoGIC scanner for Mercedes-Benz — before and after deleting error codes. After deleting the code, the indicator goes out, but the engine turnover increases slightly. After a few seconds, they stabilize, but the error code is returned, and the indicator lights up again.
To identify a faulty component, an analysis of current parameters is important through a scanner, as well as an understanding of the processes that pass within the diesel engine with the Common Rail system. The owner’s survey will also help speed up the diagnosis. Since the error code is returned again, the computer records the pressure above the specified in the ramp. The pressure in the ramp is controlled by two valves — the flow valve on the TNVD and the shut-off on the ramp. The latter is responsible for draining fuel back to the tank.
In our case, the valve on the ramp works properly. Its diversity before the error code appears is normal for idling, but after the code is appeared above. The ECU itself completely consciously increases the well, responding to a signal of increased pressure in the ramp.
Where is the problem? Does the pressure sensor in the ramp give an incorrect signal and must be changed? And the sensor changes, according to the manufacturer’s documentation, only assembled with the ramp.
It is clear that the fuel flow control valve on the TNVD is nothing. Its task to adjust the fuel stream, sufficient to start the engine, and respond to the driver’s request for the desired load. It works absolutely normal and it is not necessary to change it, like the TNVD itself.
Recall that the problem arose after washing the vehicle. Dirt disturbed during washing process gets along with fuel to the engine combustion chamber, where he burns. But since part of the fuel is given to the Magistral «Frames», then a little dirt passes through the valve of the pressure pouring on the ramp.
The task of the valve «to sign» the pressure by draining the extra fuel back to the tank. That is, it is at the very end of the hermetic contour, which creates high pressure. The valve has a mesh filter with micro cells. If you touch the grid with even clean fingers, then the valve can be disposed, since the cells from the fingers will block the cells. (Similarly, in the unrelated services, there are a lot of components, writing off sins on the poor quality of spare parts)
Return to our Mercedes. Dirt blocked the valve grid, and it stopped skipping fuel in the right amount. As a result, the pressure in the ramp was higher than the proposed, the control unit was determined and increased the unit, opening the valve more to protect the engine and at the same time normalize the pressure to the specified one. At the same time, an error code appeared with this process. In this case, repeated adaptation of the valves after cleaning the fuel system does not lead to a positive result.
Analyzing the current parameters, we advised to remove the valve from the ramp and visually examine it. The owner decided to do it on his own and later sent us the photos of the valve. On the valve clearly visible traces of corrosion in the fuel system. We recommended a neatly to wash the valve with the help of a CU cleaner, and at the same time replace the non-original fuel filter to a new and good quality. And if it succeeds, then put the valve back and delete all errors. The engine must start working properly. Otherwise, change the sensor to the new and adapt to the scanner.
After washing the performance of the valve recovered. And we got another grateful client, which was removed from expensive replacement of components «in a circle».
The author of the material