Introduction to On Board Diagnostics (II)

DiagnosticsOBD II DTCsfaults are 170-175.Sensors and ActuatorsEmployed in OBD IIDiagnosticsFuel metering actuatorPrinciple of operation The actuator used for electroniccontrol of fuel metering is the throttle body fuel injector. The TBFI consists of oneor two solenoid-operated fuel injectors that are mounted in a housing on the intakemanifold. The fuel is injected into and atomized by the moving air stream that flowsinto the intake manifold. PCM controls the amount of fuel. Fuel metering actuatordelivers fuel in precise amounts under PCM control. The amount of fuel injected intothe cylinder is determined by the length of time that the injectors are energized which istheir duty cycle. The injection time is synchronous with engine speed and is given by:intake air amount/engine speed x compensation coefficient (correction factor) +voltage-compensated injection time. Fuel trim is used to find the correction factor.Compensation coefficients are dependent on driving conditions such as heavy load,idle, or braking. Asynchronous injection is performed during start-up andacceleration. Fuel injectors are based on multipoint injection in which each eachinjector is mounted on the intake manifold of its cylinder.PCM monitors the rate of updating fuel trim and the correction factorto determine if the fuel metering actuator (and injectors ) is functioningproperlyThe failure modes of fuel system are diagnosed by OBD II. DTCs for these