How can I reset the fuel mileage on my BMW X3 2.5L 05 v6

Question

Car recently went into the mechanic for some repairs, I had a faulty ignition coils and a exaust hole almost at the engine before any censors in the system. The cars computer is reading 19.7L/100km. Obviously this is terrible fuel mileage. I’m wondering if a computer reset could alleviate this fuel issue? My theory is that that cars computer was constantly reading too much oxygen because of the exhaust hole which skyrocketed the fuel economy and now that the problems are fixed the computer is so outdated that it can’t adjust for better economy? The ABS censor rings have also rusted off the back axel causing the speedometer not to work properly. Could this also be the cause of these issues? I’ve read that taking out the battery for an extended period of time will essentially reset the vehicles computer to factory minis the accumulated kilometres. Any suggestions to fixing this problem? Like I said the car came out of the shop no more than two weeks ago so I can’t understand why the economy is still so bad. I drive it’s aggressively but not enough to cause fuel mileage as exaggerated as 19.7L per 100 km

Answer 1

1. Have you reset the mileage on the dashboard (OBC)? You should hold some button down on the fuel economy screen and it should reset. I'm assuming you've done this but the OBC persists in its reading of this high consumption. In that case, does the car actually consume this amount? Try filling the fuel tank, resetting the short-term mileage, driving 50-100 KMs and then topping the fuel tank completely up again. What amount does it take? If the real fuel consumption is within 10% of the OBC economy, then you have a sensor issue somewhere (like an oxygen sensor) or a fuel system issue. If not, the the speedometer error could cause it, but only if it's a really big error.