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Engine Performance Flashcards

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

Read the first 7 Engine Performance flashcards as text

  1. A P0420 code is set. Downstream O2 sensor voltage switches almost as fast as the upstream sensor. What does this indicate?

    Answer: The catalytic converter has lost oxygen storage capacity

    A working converter stores oxygen and smooths the downstream signal, so a downstream signal that mirrors the upstream one means poor efficiency.

  2. A P0401 code most directly indicates what problem?

    Answer: EGR flow insufficient

    P0401 is EGR flow insufficient detected, often caused by carbon-clogged EGR passages.

  3. Excessive EGR flow at idle would most likely cause which symptom?

    Answer: Rough idle or stalling

    Inert exhaust gas at idle dilutes the mixture and causes a rough idle or stalling.

  4. A P0442 code indicates which of the following?

    Answer: EVAP system small leak detected

    P0442 is a small EVAP leak, typically about 0.040 inch, while P0455 is a large leak.

  5. What is the preferred tool for locating a small EVAP system leak?

    Answer: Smoke machine

    A smoke machine pushes visible vapor into the sealed EVAP system to show exactly where it leaks.

  6. A failed PCV valve stuck open would most likely cause which condition?

    Answer: Lean idle and high idle speed

    A PCV valve stuck open lets excess unmetered air into the intake, leaning the idle mixture and raising idle speed.

  7. Which readiness monitor is continuous on OBD-II vehicles?

    Answer: Misfire

    Misfire, fuel system, and comprehensive component monitors run continuously, while catalyst and EVAP are non-continuous.