Every modern car has a computer that monitors its engine, gearbox, brakes and other systems. When something drifts out of range, it stores a fault code. An OBD scan reads those codes so a technician can see what the car has noticed.
What a scan can show
- Stored and active fault codes across the engine, transmission, ABS, airbag and body modules.
- Live readings from key sensors, such as coolant temperature and fuel trim.
- Whether a fault is current or an old, cleared event.
What a scan cannot do
A fault code points at a circuit or a system, not always at a broken part. A misfire code, for example, can come from a spark plug, a coil, an injector or a vacuum leak. The scan is the start of the diagnosis, and a technician's judgement finishes it.
When to book one
- A warning light is on.
- The car has lost power, idles roughly or uses more fuel than before.
- You are about to buy a used car.
- After a repair, to confirm the fault is gone.
What to ask for
Ask for the codes in writing, an explanation in plain language, and a recommended next step. Avoid anyone who clears the codes and sends you away without finding the cause, because the light will return.
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