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Evaporative Emission Control Systems Flashcards

7 cards from real CEI practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Why is the fuel cap the first component an inspector should check when diagnosing a P0440 or P0455 code?

    Answer: A loose, missing, or faulty fuel cap is the most common cause of large EVAP leaks

    A loose, cross-threaded, or damaged fuel cap is the single most common cause of large-leak EVAP codes because it directly breaches the sealed fuel system, allowing significant vapor escape.

  2. What is the significance of the OBD II 'two-trip' detection requirement for most EVAP codes?

    Answer: The fault must be detected on two consecutive drive cycles before the MIL is illuminated

    OBD II requires that most EVAP faults be confirmed on two consecutive drive cycles before illuminating the MIL, reducing false positives caused by transient conditions such as refueling or temperature extremes.

  3. Which tool is specifically used to verify the sealing integrity of a vehicle's fuel cap during an emissions inspection?

    Answer: Fuel cap pressure tester

    A fuel cap pressure tester applies a specified pressure to the cap and measures its ability to hold that pressure, confirming whether the cap seal is intact and capable of preventing EVAP system leaks.

  4. How does cold ambient temperature affect EVAP system monitor readiness on an OBD II vehicle?

    Answer: EVAP monitors may not run if ambient temperature is below the PCM threshold (often around 40°F / 4°C)

    Most OBD II PCMs will not run the EVAP monitor below a calibrated minimum ambient temperature because fuel vapor pressure is insufficient at low temperatures to produce reliable test results.

  5. What does it mean when an emissions inspection report shows the EVAP monitor as 'not ready' (incomplete)?

    Answer: The PCM has not yet completed the EVAP self-test during this drive cycle set

    A 'not ready' EVAP monitor status means the PCM has not had the opportunity to complete its internal EVAP self-test during the current set of drive cycles, which may cause the vehicle to fail an OBD-based emissions test.

  6. Which EVAP system fault is most likely to cause a rich running condition and poor fuel economy in addition to an EVAP code?

    Answer: Purge valve stuck open at idle

    A purge valve stuck open allows a constant flow of fuel vapors into the intake manifold even at idle, creating an uncontrolled rich mixture that causes rough idle, rich codes, and poor fuel economy alongside EVAP faults.

  7. Under California's Enhanced EVAP (OBD II) inspection criteria, a vehicle will fail if the EVAP monitor shows 'not ready' AND which of the following is also true?

    Answer: The vehicle has more than two other monitors showing 'not ready'

    California's OBD inspection allows a limited number of 'not ready' monitors (typically one for newer vehicles, two for older OBD II); if EVAP plus additional monitors are incomplete, the vehicle fails the OBD portion of the inspection.