OBD-II Codes

OBD-II codes are part of the self-diagnostic system that all cars come with. The OBD system uses Diagnostic Trouble Codes (DTC) to tell you which specific component has an issue. They’re five-digit codes and are made up of four different subsets of codes that indicate where in the vehicle the malfunction lies (for example, P1234).

The first number in the DTC tells you if the code is specific to the vehicle manufacturer or a generic code that applies to all OBD-II systems. The last three numbers tell you specific information on the vehicle system or circuit that is running into trouble. The first of these subsets is the powertrain, or P codes, and is the largest of the four categories. This is followed by network and integration (U), body (B), and chassis (C) codes.

The P codes deal with the powertrain system of the vehicle, which includes the engine, transmission, and any associated drivetrain accessories. P codes can be further broken down by where the numeric total after the P lies in the OBD-II code list:

• P0100-P0199: Deal with fuel and air metering and monitor the vehicle’s fuel mileage and emissions systems. Parts like the oxygen sensor lie within this subset of P codes as well as parts controlling air-to-fuel ratios in the vehicle.
• P0200-P0299: Associated with the fuel injector circuit and will only include parts like the fuel injectors.
• P0300-P0399: Indicate issues with engine misfiring so they typically include parts like spark plugs or ignition parts.
• P0400-P0499: Deal with auxiliary emissions controls like the EVAP (Evaporative Emission Control) system. The EVAP functions by preventing gas fumes from reaching the outside atmosphere and keeping air pollution to a minimum.

The next couple of P code subsets have to deal with a vehicle’s computer systems:

• P0500-P0599: Deal with the vehicle speed controls and idle control systems. Typically, issues with the vehicle speed sensor (VSS) will trigger these codes on the vehicle.
• P0600-P0699: Computer output circuit problems and any issues stemming from a faulty computer system will trigger these codes.
• P0700-P0899: Specifically indicate problems with the transmission system and any related components. Since these codes monitor the functioning of the transmission, their appearance typically relates to faults in the computer that control how the transmission operates.

For more information on further diagnosing your vehicle’s transmission issues, visit KBB.com’s transmission repair guide.