the codes are never to be considered diagnosis. as mentioned by twitchkitty.

the codes are just flags for systems that reportedly failed or some check didnt pass.

e.g. chevy 3.4 use 2 crank sensors, one to time the engine to start and one to fine tune the system for sequential injection, if you see the fine tune sensor pop an error and you shoot to replace it because "computer said it" - you have a 50% chance of repair.

WHY you ask - lets take an example I had.

This certain car had a very slow coolant leak at the bypass tube which sits right infront of the cam sensor connector, the leak would sometimes spray coolant into the connector essentially drowning the connector. The reference voltage for the cam and fine tune crank sensors are shared circuit, if one sensor leg shorts it (that coolant leak bridged it to ground) out the crank sensor will stop working too, In 50% cases the code shows up as crank sensor - the other half shows up as cam sensor. If the main timing sensor fails or shorts, it gets more interesting and involved to sort out as the engine doesnt fire at all.

The actual fault above was the coolant leak.

another example - toyota camry 2004 2.4 litre motor - code P0171 - system lean - you need to see the long term and short term fuel trims to diagnose this, in some cases its a dirty/failed MAF sensor and in some cases its a leaking intake manifold gasket. The diagnosis will determine what has failed.

similarly cylinder misfire can be misleading - you need to know how it registers the misfire code, e.g. toyota use a feedback system from the coil to confirm the ignition event, messed up feedback signal will immediately light the CEL, it takes quite a lot of fuel related misfire to log a code on a toyota OTOH MB 112 engines dont use feedback but rely on the acceleration events of the crankshaft sensor to determine which cylinder is done firing correctly - so in this situation fuel, spark or even dodgy compression (dirty valves) can trigger that CEL. - Then comes the part if the crankshaft position sensor was calibrated when installed,otherwise it can be throwing a P0304 while the misfire could be anywhere between 0301-0306

There is a fine line between shotgunning parts and diagnosing.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)