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OBD fault codes: what each one means

When the engine warning light comes on, the ECU stores a code that indicates which system has failed. Look up yours to find out what it means, its most common causes, whether you can keep driving and which known faults of each engine cause it.

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Frequently asked questions

What is an OBD fault code?

It is the code the car's ECU stores when it detects a fault in a system monitored by on-board diagnostics (OBD). It starts with a letter indicating the system (P: engine and transmission; C: chassis; B: body; U: communications network) followed by four characters. If the second is a 0, the code is a generic SAE standard code and means the same on all makes; if it is a 1, it is specific to the manufacturer.[1]

Which cars have OBD diagnostics?

In the European Union it was required by Directive 98/69/EC, and the European standard (EOBD) applies to passenger cars registered from 1 January 2001 with a petrol engine and from 1 January 2004 with a diesel engine.[1][2]

How do I read my car's fault code?

With an OBD2 reader plugged into the car's diagnostic socket, or at any garage. The code indicates the system and the type of fault the ECU has detected, not always the part that has failed: on each page we explain the possible causes and in what order to check them.[1]

Sources

Every fact on this page links to its source. If you find an error, let us know.

  1. On-board diagnosticsWikipedia · Other source · consulted 2 October 2026
  2. OBDWikipedia · Other source · consulted 2 October 2026 · in Spanish