I hear you but here's where they go wrong... Most likely there was an event that either caused the lean condition for which there may be a code. Or that there is a sensor malfunction that would cause it to happen. You said you were on a hard pull when it happened? Did the car go into limp mode and not want to rev past a certain RPM until you shut down and restart? I am pretty sure I know what it is but unless your reader can retrieve BMW codes it won't give you the entire picture, herein lies my issue with generic code readers.
A code is a code, it doesn't matter whether you use a Peake tool or any other, you're going to get the same code. All it is doing is retrieving a stored error from a computer. The problem is that there are BMW specific codes that they can't read - it'll probably report back that it is a proprietary code or worse not say anything at all.
What's so bad about seeing a good trustworthy (key word, trustworthy) independant? (I am one so I am biased) if they have the right tools and experience / training.
EDIT: We have over the years had people come in and request parts to be installed based on what they found online or what their handheld told them. We tell them that we'd like to perform some diag first, we get turned down. We replace the part, problem not fixed, customer gets upset at us. Not to say that there isn't good information to be had.. this board being one of the better sources, the group experience is deep here... I sound like Yoda
I'll take a bit of issue with this. Here is why:
You are saying you don't like any 'generic code reader' for reasons unrelated to reading codes!
A code reader is essential for DIYers. Period. Peake is the best BMW-code-specific reader on the market, given the resource base.
Is there a better tool for a DIY to diagnose? Love to hear of one!
Now, here is the essential part that gets at the core of your issue with a generic reader: people must understand their limitations.
(It'd be like saying "Adjustable wrenches are no good, when you put too much force on them you can strip a head, only use a 6 point box end"...the truth is an adjustable wrench is fine for it's intended use.)
Take me. I read codes, used a generic scan tool and exhausted my troubleshooting. I brought it to your shop for a smoke test, and to diagnose the lean condition. A vanos test later we had the culprit..
From YOUR seat- and there are a few guys on the board that are your doppelgangers, (they have shops and are indys)- it is really quick and easy for them to spot issues quickly and easily... BUT the real truth is that most Indys are no better than many DIY hacks here. The consumer has no clue how to FIND a 'trusted indy'... We see these stories all the time.
Indeed, shops will say "replace the Vanos" when simply a solenoid O ring change might do it. I can understand why- as a shop you don't want to waste hours on a job- even though you clearly told the customer 'it might not do it'- only to find that was not the whole problem and more work is needed. But shops will also say "cats are bad" when it may be something else, or insist the misfires must be plugs or coils...
In the end, the code reader is only part of the equation, and the DIYer must balance cost against 'perfect info'.... I usually advise certain items be replaced to chase codes, but ONLY if they are 'maintenance' or wear items, or low cost. Once you get to a point it is no longer cost effective and the profession computer is needed.
The trick, of course, is in that "trustworthy' part you cited....