DOBD DashX ☰ Browse all codes Blog

OBD-II guides

Reference pages on how OBD-II works: the connector, the codes, the monitors and the sensors.

What is OBD-II?

OBD-II is the self-check system in a car's engine computer. It watches emission-related parts, lights the check engine light and stores codes any scan tool can read.

OBD-II connector pinout and location

The OBD-II port is a 16-pin SAE J1962 socket near the driver's knees. Here is what every pin does, which pins each protocol uses, and where to find the socket.

History of OBD-II

How on-board diagnostics went from California's OBD I in 1988 to OBD-II on every 1996 US car, EOBD in Europe, CAN in 2008 and permanent codes from 2010.

Drive cycles, readiness monitors and emissions tests

Why an OBD-II car shows monitors 'not ready' after codes are cleared or the battery is replaced, how many an emissions test allows, and Ford's published drive cycle.

How to read an OBD-II code

An OBD-II code like P0301 has five characters: the system, whether it is generic or maker-specific, the subsystem and the exact fault. Plus pending, confirmed and permanent codes.

Oxygen sensors explained

What an oxygen (O2) sensor does, upstream vs downstream, bank 1 sensor 1, narrowband vs wideband, the codes it sets, why sensors fail and how to check one.

OBD-II glossary: acronyms and terms

Plain definitions of the acronyms and terms you meet when reading OBD-II codes: MIL, DTC, PCM, MAF, EVAP, EGR, freeze frame, readiness, pending codes and more.