🔍OBD-II Scanner / Code Reader

An OBD-II scanner is the first thing you plug in when the check-engine light comes on — it pulls the trouble codes the car's computer is already storing and tells you whether you're chasing a loose gas cap or a failing O2 sensor. Cheap Bluetooth dongles paired with a phone app are fine for code reading and clearing; spend more if you want live data streams, bidirectional control (commanding the cooling fan, cycling the ABS pump), or manufacturer-specific codes. Pair with a multimeter — codes point you at a circuit, voltage tells you what's actually wrong.