A DTC — Diagnostic Trouble Code — is how a control unit reports a fault it detected. When a sensor reads outside its expected range, or a plausibility check fails, the unit stores a code and usually lights the dashboard.
Generic OBD-II codes follow a pattern: P0401 — P for powertrain, then four
digits. Manufacturer-specific codes carry more detail and are the ones that actually tell you
what happened.
Pending codes have been seen once and are waiting for confirmation. Stored codes are confirmed. Permanent codes cannot be cleared with a scan tool at all — they clear themselves only after the unit has seen the fault stay away across several drive cycles.
Clearing a code does not repair anything. If the cause is still there, the code comes back on the next drive cycle, and clearing also resets readiness monitors — which matters at inspection time.
Turning a code off inside the software is a different operation again. It is used where the underlying component has been legitimately removed or replaced, and it is your responsibility to confirm that the change is lawful for the vehicle's intended use.