Introduction to On Board Diagnostics (II)

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Functionality of PowertrainControl Module (PCM) inOBD II DiagnosticsPerform powertrain control functions to reduce emissionsand meet OBD II regulations.Idle Speed Control: When the throttle angle reaches its closed positionand engine RPM falls below a preset value (about 600), the PCM switchesto idle speed control mode. The PCM controls the idle air controlpintle (valve) to let air to flow into intake manifold, bypassing the closedthrottle to prevent the engine from stalling due to lack of torque. Thepintle is operated by a stepper motor, which withdraws the pintle from itsclosed position (seat) to open the bypass that lets a limited amount ofair flow into the intake manifold. Idle speed is detected by the RPM sensorindicating a low value, the vehicle is stationary, and throttle is closed. ThePCM adjusts the pintle to keep the idle speed around 600 to 700 RPM. Thepintle valve is completely closed when engine is not idling.
Functionality of PowertrainControl Module (PCM) inOBD II DiagnosticsPerform powertrain control functions to reduce emissionsand meet OBD II regulations in closed-loop loop control.EGR Control: At high engine load (high throttle angle), and high Engine RPM,and at high engine coolant temperature, the cylinder temperature at combustionreaches temperature greater than 3000 0 F which causes NOx emissions to increasebeyond the OBD II limits. For this reason, the PCM recirculates a small portion ofthe exhaust gases into the intake manifold. This has the effect of reducing oxygencontent without reducing the mass of gas processed. The combustion impartsenergy to the inert exhausts gas as well as to the air charge. The net effect isto retain much of the engine power while reducing the flame temperatureat part load, thus decreasing production of NOx. The PCM controls the EGRvalve depending on the throttle angle, engine RPM, coolant temperature. EGR iscompletely closed during cold start and during start up of the engine.The duty cycle of the EGR valve is obtained from predefined table lookup.
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Introduction to On BoardDiagnostics
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OBD II monitors more components and
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Powertrain and EmissionControls in
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Powertrain and EmissionControl in P
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OBD II for L & MD VehiclesSTD Manua
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OBD II for L & MD VehiclesDiagnosti
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Fundamentals of PowertrainControl s
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The Freeze Frame can also be used f
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Evaporative System Monitoring: Hydr
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OBD(II)In addition the electrical c
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Introduction to On Board Diagnostics (II)

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