Significant Decline in Fuel Efficiency of BMW F10 520D

[MDMH757]

My car has recently encountered a significant problem with excessive fuel use. I previously achieved a minimum of 450 miles on a half tank, but now I am only attaining approximately 300 miles at best, and I am uncertain as to the reason. The vehicle receives a full tank and undertakes a 300-mile motorway excursion weekly.

I regularly undertake extended motorway drives at 70 mph for over three hours, so I doubt it could be the DPF, although I am not totally certain. I previously had an exhaust back pressure sensor problem that resulted in a powertrain fault on iDrive; however, after replacing the sensor, the vehicle no longer displays that fault. I have poured DPF cleaner to a full tank and executed another thorough drive on the freeway, but to no avail. I have recently undergone a significant service that has yielded no results.


I consulted BimmerUtility, which indicates my soot levels are at 45.99g. I have observed this value decrease to 8g, but it occasionally spikes to the high teens or abruptly returns to approximately 45.99g. I previously had a 24C800 error, which was resolved by replacing the sensor. However, I am now facing a 25C800 error. Does this indicate that the DPF need replacement and is it the source of the problem?

[HOV]

Verify if the pre-turbine pressure sensor pipe is unobstructed; if it is clear, replace the sensor and reset the settings.

It is also advisable to inspect the brakes to ensure none are binding, as this significantly impacts fuel economy.

[MDMH757]

Is the pre-turbine sensor pipe the conduit that links to the exhaust back pressure sensor? Upon inspection, it appears to be clear. I also inspected the brakes, and they are in satisfactory condition.

[HOV]

The steel pipe originates from the banjo bolt on the manifold, with the sensor inserted into a little rubber part at the end.