Driver's guide
How to read and clear your car's fault codes
Cars sold in the EU have a standard diagnostic socket (EOBD): gasoline cars since 2001 and diesels since 2004. With it you can see what the car has recorded.
Reviewed by Daniel Morales, founder of Reprorace SL, on
The OBD socket: where it is
It is a 16-pin trapezoid connector, almost always under the steering wheel at the height of the driver's knees; sometimes it is behind a cover in the center console or in the glove box.
OBD-II (United States) and EOBD (Europe) are in practice the same standard: the same connector and the same generic codes.
What you need to read the faults
An OBD reader: from a handheld scanner to a connected device such as the ECO-LITE, which stays plugged in and shows you the faults on your phone or computer.
With the ignition on or the engine running, the reader asks the engine control unit and, depending on the device, the other control units (gearbox, ABS, airbag…).
How to read a code
Every code has a letter and four characters. The letter tells you the system: P engine and gearbox, C chassis, B body and U the communication network between control units.
The first digit tells you whether it is generic (0, the same meaning on every make) or the manufacturer's own (1). The rest identifies the component and the type of fault.
Besides the code, the car records whether the fault is active or old (stored) and a "freeze frame" with the data from that moment: engine speed, temperature, road speed…
Clearing faults: when to and when not to
Clear only after writing the code down and, ideally, after the repair. Clearing fixes nothing: if the fault is still there, the light will come back on.
Clearing turns the light off, but it also deletes the freeze frame and the readiness monitors. Until the car completes its drive cycles, it may fail its technical inspection.
Do not clear airbag, brake or steering faults to get rid of the warning: take the car to a workshop.
After clearing, check again
Drive normally for a few days (town, open road and a cold start or two) and read the faults again. If the code is back, the fault is still there.
With the ECO-LITE, after every clearing the device reads the faults again and tells you whether they were cleared and how many remain.
Got the code?
Look it up in the glossary: what it means, common causes and whether you can keep driving.
Read your car's fault codes on your phone
With an ECO-LITE in the OBD socket you see the codes in your account, with the data captured when the fault happened, and your workshop can check them remotely, always with your permission.
Keep reading
- OBD fault codes: what each one means
- Check engine light on: what to do
- Will your car pass its MOT or inspection with the engine light on?
- Wi-Fi OBD2 reader: which one to choose
- Reading fault codes by car make
- Remote OBD diagnostics: what it is, how it works and what it can't do
- Vehicle diagnostics glossary