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Evaporative Emission Control Systems Flashcards

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  1. What is the primary purpose of an evaporative emission control (EVAP) system?

    Answer: To prevent fuel vapors from escaping into the atmosphere

    The EVAP system captures and stores fuel vapors from the fuel tank and fuel system, preventing them from venting directly into the atmosphere and contributing to hydrocarbon emissions.

  2. Which component in the EVAP system stores fuel vapors before they are purged into the engine?

    Answer: Charcoal (activated carbon) canister

    The activated charcoal (carbon) canister adsorbs and temporarily stores fuel vapors from the fuel tank until conditions allow them to be drawn into the engine and burned.

  3. What is the function of the purge valve (purge solenoid) in an EVAP system?

    Answer: It controls airflow from the canister to the intake manifold

    The purge valve, controlled by the PCM, opens to allow stored fuel vapors in the charcoal canister to be drawn into the intake manifold and burned during normal engine operation.

  4. A vehicle sets a P0442 diagnostic trouble code. What does this indicate?

    Answer: EVAP system small leak detected

    P0442 is defined as 'Evaporative Emission Control System Leak Detected (small leak),' indicating the EVAP system cannot maintain pressure, typically caused by a leak equivalent to a 0.020-inch orifice.

  5. What does the fuel tank pressure (FTP) sensor measure in an EVAP system?

    Answer: Pressure or vacuum inside the fuel tank

    The fuel tank pressure sensor monitors the pressure (positive) or vacuum (negative) inside the fuel tank, providing the PCM with data needed to perform EVAP leak detection tests.

  6. Which of the following conditions is typically required before the OBD II EVAP monitor will run?

    Answer: Fuel level between 15% and 85%

    Most OBD II EVAP monitors require a fuel level between approximately 15% and 85% to ensure there is enough vapor to detect leaks while avoiding inaccurate readings from an overfull or nearly empty tank.

  7. What does a P0455 diagnostic trouble code indicate?

    Answer: EVAP system gross (large) leak detected

    P0455 indicates an 'Evaporative Emission Control System Leak Detected (gross/large),' meaning the EVAP system has a significant leak, often as large as a missing or loose fuel cap.