It knowing how to read it
Iv had it heaps of times with bmw petrols common as anything with bmws,
system too lean bank 1 and 2, and random missfires on all 6 cylinders, then people load the parts cannon and assume lambdas or mafs coils or spark plugs and then must have a vacuum leak,
Take a step back get on live data, lambdas are reading so why do they need changed? Bank 1 and 2 wont pull a lean code for fun,
Maf readings are within spec so why did you change it?
people load the parts cannon again and assume it needs injectors,
Iv replaced all these parts and these codes aren't going why?
Get on live data its opening the injectors for longer then normal conditions Its giving a lean condition instead of a rich condition? Yes
Lambdas and maf are working and reading and responding to changes in engine rpm Yes?
Ok so your cars telling you its not getting enough fuel have you checked fuel pressure? 'No there isnt a code for it'
Check it and find out a 50.8psi system is only pumping 30psi at the fuel rail, Takes all of 15mins and is cheeper to get it diagnosed then spend 300+ quid on the parts cannon for fun,
Another example,
My girlfriends dads mini 1.6d with the pug dv6 engine, broke down 50miles from home I got a pal in the city to tow him off a busy road and have a quick check before i head in to it as it was a 100mile round trip with the trailer regardless,
It had a crank sensor fault, and an egr fault, okay no biggie 18 quid for a crank sensor and a 10mm socket with me il take one with me incase and if the egrs a problem unplug it and get it home in limp mode if needs be,
Got in went to start it no tacho movement while cranking, okay il throw crank sensor on, no change so throw it on trailer and take it upto workshop, after 30mins poking about noticed the crank sensor wasnt getting voltage neither was the egr or cam sensor or an intake boost sensor, or intake flap,
A check on ecu fuses showed that it was getting reverse polarity earth through 2 fuses,
After a hour of stripping the ecu tray and bits out the way
Turned out a mouse had been nibbling at the loom under the battery and had a nest there, And because of the short the ecu wouldn't turn one of its internal realys on,
4 hours later few wires in situ repaired and running still with its original crank sensor and egr valve,
