Klaro

OBD2 fault codes

Generic codes mean the same thing on every car. Find yours in the matching family.

P00xx — Fuel and air metering, auxiliary emission controls

This family covers the measurement of incoming air and injected fuel, together with the emission devices attached to them. A fault here distorts the mixture the engine burns, which costs fuel and raises emissions.

P01xx — Fuel and air metering

These codes concern the sensors that tell the control unit about the mixture: mass airflow, oxygen sensors, fuel trim corrections. They often point to an air leak or an ageing sensor rather than an outright failure.

P02xx — Injector circuit

These codes point directly at the injectors and their electrical control. An injector that no longer sprays properly unbalances combustion in its cylinder, and usually brings misfire codes with it.

P03xx — Ignition and misfire

This is the most serious family of the set. A misfire sends unburnt fuel into the exhaust, where it destroys the catalytic converter within a few dozen kilometres. A flashing warning light means a misfire is happening now: stop driving.

P04xx — Emission controls

Catalytic converter, exhaust gas recirculation, particulate filter, fuel vapour. These faults rarely leave you stranded, but they fail the roadworthiness test and become expensive if left alone.

P05xx — Idle speed and vehicle speed control

Unstable idle, cruise control, auxiliary inputs to the control unit. These codes show up as erratic behaviour at a standstill, or a function that refuses to engage.

P06xx — Control unit and output circuits

Faults internal to the engine control unit or to its output circuits. Before suspecting the unit itself, which seldom fails, check grounds, connectors and battery voltage.

P07xx — Transmission

Automatic or automated gearbox: ratios, clutches, speed sensors. These codes often come with a limp mode that locks the box in a single gear.

P08xx — Transmission (continued)

A continuation of the previous family: transmission controls, solenoids and sensors. Diagnosis nearly always requires the manufacturer's documentation.

P09xx — Transmission and controls

The last transmission-related series, including gear selection controls. Like the previous one, it belongs in a workshop rather than a roadside fix.