OBD CodesLearn about fault codes
Short guides in plain language for car owners.
How to read an OBD-II code
An OBD-II code such as P0171 has five characters, and each one means something. Learn what the letter and the digits tell you about the fault.
The check engine light: what it means and what to do
Why the check engine light comes on, the difference between a steady and a flashing light, when you must stop, and the simple checks to do before the workshop.
The OBD port and scan tools
Where to find the OBD-II diagnostic socket in your car, what a code reader, a Bluetooth adapter and a full scan tool can do, and how to read codes yourself.
Clearing codes and readiness monitors
What happens when you clear a fault code, why the light comes back, what readiness monitors and drive cycles are, and why disconnecting the battery is a poor fix.