If you purchase a scanner, be sure to purchase one that is capable of reading livestream data. (Hint: code-only cheapie 'scanners' can't.) The reason: OBD-II DTCs (Diagnostic Trouble Codes) will only tell you what sensor or system is reporting a problem, but not necessarily what the problem actually is.
For example, seeing a P0171 or P0174 (which are "bank 1 oxygen sensor/system too lean" or 'bank 2 oxygen sensor/system too lean," respectively) usually prompts the reaction "replace an oxygen sensor." However, the oxygen sensor(s) might be picking up something else. By looking at the livestream data, you can see what the oxygen sensors are doing, and if you see both P0171 and P0174 and your long-term fuel trims are strongly positive (15+%) but the upstream oxygen sensors are switching like they should (0.0-1.0VDC, switching rapidly) and the downstream sensors are tracking accordingly (0.0-1.0VDC, slowly following the upstreams like a rolling average), you've got a vacuum leak somewhere, not bad sensors. If there's also a P0300 ("random misfire"), it's a really bad vacuum leak (e.g., intake gasket failure). Otherwise, check for things like collapsed rubber PCV elbows, broken vacuum lines, etc.
A modern car's engine management system operates on a giant feedback loop, where the MAF/MAP/AIT sensors tell the powetrain computer what's coming in, the TPS tells it what the engine is being told to do by the driver, and the oxygen sensors monitor catalytic converter performance and detect the backside results from air/fuel combustion. Understanding how the system works, and being able to inspect what each sensor is reporting while the vehicle is running, are critical keys to finding and fixing problems.
IMPORTANT NOTE: Any religion-related posts I make are as a member and not as a forum staffer, and are not intended to promote any specific agenda or doctrinal understanding as official or unofficial board policy. Official staff actions on my part will always be clearly marked as such.
Deja moo - the feeling you've seen this bull before...
"Political Correctness is a doctrine fostered by a delusional, illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."