1999 BMW 540i • 67,000 miles

Scan tool read two codes. PO 170 and PO 173. Fuel trim malfunction. Vehicle starts and idles good. In driving I have not noticed any hesitation. I have read blogs on other sites and a variety of things are pointed out. Im hoping you can narrow the options. Thank you
Hot 540
February 15, 2012.

Both of those are fuel trim exceeded codes. P0170 is for bank 1 and P0173 is for bank 2. What this means is there is a perceived or actual problem with the vehicle resulting in a rich or lean condition. The computer has compensated by adding or lowering the amount of fuel the vehicle receives by more than 24%. Anything under 24% and there is no code set. Honestly, without a professional performing various pinpoint tests and examining the engine data, there is no other way to narrow this fault down. My advice is to seek out a BMW specialist for this one.

Feb 15, 2012.
A BMW specialist indeed! If there is history on the replacement of the PCV plate or the throttle body profile gasket(or lack thereof) then I would start there. PCV plate on the back of the intake manifold fails at age and mileage indicated.

Dr. Hagerty
Feb 29, 2012.
Thanks for your inputs. I had the issue checked out by a BMW specialist and he suggested I replace mass air flow sensor. I have put over 100 miles on the mistress and no check engine light. Ha, ha. Problem solved.

Hot 540
Mar 19, 2012.
That is absolutely phenomenal news, Hot 540. I am glad to hear you went to a specialist that seems to have rectified your issues. Check engine lights on all cars are kind of a crap-shoot without true diagnostic data and pinpoint testing, yours is a true case of exactly that. Without any data, I would have shot at the fuel system first, here is turns out the MAF sensor was likely sending out errant readings, causing the computer to modify the fuel trim for the errant readings.

Though we couldn't help directly, I am glad that we were at least able to indirectly help : ).

Mar 19, 2012.