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How to connect a scan tool How a P-code is built Scan tools
Every car sold in the United States from model year 1996 reports its faults the same way: a scan tool on the connector under the dash reads a P-code. Enter the code the tool displays.
Look up a fault code
OBD II, model year 1996 and later, any make: enter the P-code your scan tool displays (P0420). Codes beginning P0 are the generic set, defined the same way for every make; codes beginning P1 are the manufacturer's own and are read here only digit by digit.
How a P-code is built — the full key
First digit — the system
- Pxxxx — powertrain
- Bxxxx — body
- Cxxxx — chassis
- Uxxxx — future systems
Second digit — who defined it
- P0xxx — Government required codes
- P1xxx — Manufacturer codes for additional emission system function; not required but reported to the government
Third digit — the subsystem
- Px1xx — measurement of air and fuel
- Px2xx — measurement of air and fuel
- Px3xx — ignition system
- Px4xx — additional emission control
- Px5xx — speed and idle regulation
- Px6xx — computer and output signals
- Px7xx — transmission
- Px8xx — transmission
- Px9xx — control modules, input and output signals
The fourth and fifth digits designate the individual components and systems.
What is generic, and what is not
A code beginning P0 is defined by the standard (SAE J2012) and means the same on every make: P0420 is the catalyst below its efficiency threshold on a BMW as on a Volkswagen. A code beginning P1 is the manufacturer's own: the same number means one thing on a Volkswagen and another on a BMW, so this page reads it only digit by digit. The makes also keep fault codes of their own behind the P-codes (a BMW dealer tool shows them as hexadecimal numbers); those are in the car's repair manual, not here.
Codes by marque
Scan tools and where to get them → factory and aftermarket tools; the supplier list.
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