The fuel economy of the 2012 W204 C220 with the OM 651 engine is quite poor.

[VibrantShin]

Greetings, everyone.

I am a new user, however I have been observing the community for a considerable period of time without actively participating.

I am the second owner of my C220, which has been meticulously maintained since it was new. Frequently attended to by me. The only problems I have had are linked to the DPF (Diesel Particulate Filter). I had to replace the differential pressure switch once. I have undergone a replacement of the timing chain and tensioner as well. The current mileage is presently at 196,000.

The car previously attained a satisfactory fuel efficiency rating. Some time ago, I brought my vehicle in for an airbag recall and specifically requested that they refrain from doing the emissions software update. However, they went ahead and carried out the update against my wishes. Since then, I have seen a significant decline in fuel efficiency.

I am curious if the problem is just caused by this software upgrade, or whether there is another underlying issue. I own the icarsoft mb2.0 diagnostics tool and have been examining it for indications. The only problem I have identified is a defect with the Y85 EGR cooler bypass switchover valve, with error code 53336/6058. The vehicle performs smoothly, with enough horsepower and no other defects. I have examined the diagnostic data under load and full acceleration. The vehicle performs admirably without any issues, with a boost pressure of around 2.7 bar.

I have observed that the Diesel Particulate Filter (DPF) tends to reach its maximum capacity rather rapidly, around 1% each mile, which seems to be a high rate. I am wondering whether this frequent occurrence of DPF regeneration might be negatively impacting fuel efficiency. I get that it utilises fuel for regeneration, therefore making this scenario possible.

Could the high mileage of 196k and the assumption that the DPF has not been replaced since new perhaps cause problems? I have attempted to use injector fuel additive and other similar products, but I have not had significant results.

When I say the vehicle functions properly, I mean that the temperature rises rapidly and stabilises at 90 degrees, indicating no issues. There are no leaks, and the car drives splendidly except for the disappointing miles per gallon (MPG) I am obtaining, which is around 400 to 450 miles per full tank. The fuel usage was accurately calculated to be around 37 miles per gallon throughout the whole tank. The tyre pressures are within the acceptable range, and there are no issues with dragging brakes or any other problems.

I am curious if the Y85 is responsible for the problems, or whether it is just due to the emission upgrade.
Assistance is requested.

Thank you.

[Cleverco]

Unfortunately, I am unable to assist with the diagnostics. However, if you do a search on this platform or in general, you will come across several instances of fuel consumption problems associated with the software update.
I recall a member elucidating the reason for this occurrence.
Best wishes

[Shmoein]

At what temperature does the engine operate? Does the temperature reach 90 degrees within about five minutes and remain at that level in both urban areas and on the highway? If the thermostat is not functioning properly, it might lead to increased fuel use. The software upgrade is also notorious for being a significant factor in its deterioration.
 

[VibrantShin]

Greetings, Yes, the temperature rises adequately and stabilises at 90 degrees or little above.

 

[Ledgerciao]

If the low fuel usage problem arose subsequent to the Dieselgate software upgrade, then pursuing other explanations may be futile.

Furthermore, does your vehicle own an automatic gearbox? Based on my comprehension, the update is responsible for forcing the gearbox to change gears at faster engine revolutions compared to its previous behaviour. This alteration may account for the subpar fuel efficiency. Does the automobile engage its highest gear (7th) while maintaining a speed of 70mph?

[Captiva]

Is the fuel consumption higher according to the display or when measured from a full tank to a full tank?
Has the upgrade resolved the issue with the reading accuracy?
During my recent journey to the Lake District, the onboard display indicated an average fuel efficiency of 59 miles per gallon for a distance of around 200 miles. However, upon returning home, I filled the tank to its maximum capacity and calculated the real fuel efficiency to be around 45 miles per gallon, which significantly deviates from the shown value.
The model of the car is B200 and it was manufactured in 2012.
 

[Ledgerciao]

I am uncertain about the precision of the onboard computer's computation of miles per gallon (mpg). Similarly, I am unconvinced that the accuracy of the 'brim-to-brim' method has been definitively established.

Is the filing station and the pump the same? Was the nozzle placed in a consistent manner and activated simultaneously? Undoubtedly, the ambient temperature might also have an impact.

Allow me to explain that I am not asserting with certainty which of the two approaches - onboard computer or brim-tothebrim - is more dependable. My point is simply that I fail to comprehend why individuals presume that brim-to-brim is a precise gauge.

EDIT: I will search on Google to see whether anybody has conducted an experiment to establish it...

 

[Shmoein]

Both the onboard computer and brim-to-brim method use the car's odometer to determine the mileage. Therefore, the issue at hand is which of these methods provides a more precise measurement of fuel consumption: the pump or the car's fuel system?

 

[Ledgerciao]

One may argue that if both vehicles use the same odometer, then this would not impact the disparity, since the precision or imprecision in the mileage measurement will remain consistent.

Regarding the statement "metres fuel more accurately," it is indeed true, but it is not the only deciding factor. While the pump itself may be precise, the process of calculating whether a tank is completely filled may introduce inaccuracies.

[Mantelle]

It is probable that the problem has been caused by the software downgrade. I have had several instances of such occurrences involving subpar performance and abysmal fuel efficiency after the software downgrade. Upon taking my vehicle in for the airbag recall, I explicitly informed the customer care representative and then sent them an email to clarify my preference of not making any changes to the software. They verified that this was OK.
Upon delivering the automobile, I took the initiative to verify once again that no software modifications would be made. Surprisingly, they had no documentation of my previous refusal, but assured me that it was OK to decline the software upgrade. I ensured that they explicitly documented on the service sheet that no modifications to the programme were to be done. In addition, I covered the OBD port with adhesive tape and attached a written message instructing others not to interact with it.

I am quite certain that they made no alterations. Only the airbag recall was performed.

At a temperature of 196K, it is quite likely that the diesel particulate filter (DPF) is significantly filled and may need removal and cleaning. Over time, DPFs tend to get obstructed.

My vehicle is a C250 with the same engine. Typically, I can go around 450 miles on a full tank of petrol. However, I must admit that I like to drive with enthusiasm rather than focusing on fuel efficiency.

If the gearbox is retaining the gears for an extended period of time after the software modification, doing a gearbox reset might be beneficial and straightforward to execute. May or may not have an impact. To reset the gearbox of a W204 vehicle, search for instructions on Google.

Wishing you success and favourable outcomes.

[VibrantShin]

No, the gearbox remains same. I am still able to smoothly engage 7th gear on the motorway in similar conditions.

I have computed the miles per gallon (mpg) by measuring the fuel consumption from a full tank to another full tank and by using the car's built-in mpg calculations.

It is possible that the Diesel Particulate Filter (DPF) is completely filled, yet the diagnostic report indicates just 2 grammes of ash and 1 gramme of soot.

[Captiva]

Are you suggesting that the brim to brim method and the car's computer are both measuring MPG in the same manner?
The mine is located far away.

[VibrantShin]

No, they are not identical.

Utilising mileage and fuel receipts to their fullest extent ensures precise and optimal performance. I often engage in this activity.

[Captiva]

What was your fuel efficiency prior to the update?
Was the prior fuel efficiency assessed using the method of filling the tank to its maximum capacity and comparing it to the amount of fuel consumed? Additionally, how much farther does your dashboard display indicate compared to this measurement?

[Ledgerciao]

Indeed, it is capable of doing that, but the crucial inquiry is to the velocity at which it transitions into 7th gear. Specifically, does this occur when the vehicle reaches a speed of 70 miles per hour?

[VibrantShin]

Yes, as per usual.