Lane Keep Assist, Adaptive Cruise Control, AEB via OBD-II: typical codes U0428, C1B01, why calibration is needed after windshield replacement, and why an OBD adapter won't do it.
What OBD-II shows about the AC system: codes B1234, B10DA, high/low-side pressure, evaporator temperature, why "just add refrigerant" isn't always the answer, and how to diagnose the compressor clutch.
Why Auto Start-Stop suddenly stopped working, how OBD-II shows the status (Ready/Not Ready), ECU criteria for the stop, the role of the EFB/AGM battery, and how to diagnose via live parameters.
What OBD shows about AT: codes P0700, P0741, P0742, adaptation values, ATF temperature, why "sealed for life" is a marketing myth, and how to diagnose slip.
What OBD-II says about the battery and alternator: codes P0562 (low voltage), P0563 (high), P0620 (alternator). How to read system voltage and why "overcharge" is more dangerous than "undercharge".
What BCM does, how OBD-II reads B-codes and U-codes, why "the window is stuck from pause" is often the BCM, and how to tell the module from a wiring fault.
The most useful OBD-II PIDs for daily monitoring: LTFT, coolant temp, MAF, boost pressure, misfire counter. How to set up automatic logging in Car Diagnostics and what to do with the trends.
What OBD-II shows about brake pads on modern cars: wear sensors, calculated brake pad wear, codes C1000, C1100, and why "2000 mi to replacement" on a BMW is not guesswork.
Plain-English CAN Bus: how 60+ ECUs communicate over 2 wires, what ISO 15765-4 and ISO-TP are, high-speed vs low-speed CAN, and why "lost communication with ECU" (U0100+) is critical.
What CAN-FD (Bosch, 2012) is, how it differs from classic CAN, why Tesla, Ford Bronco, BMW 2020+ need new OBD adapters, and how to check if your ELM327 supports CAN-FD.
Step-by-step algorithm for "no-start": how OBD-II tells in 5 minutes whether the issue is the immobilizer (P1602, B10CC), fuel pump, starter, battery or ECU.
What OBD-II can do on Chery Tiggo, Geely Coolray, BYD Tang, Great Wall Haval: SAE J1979 standard, custom PIDs, GB codes, brand tools vs universal ELM327.