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OBD Systems & Diagnostics Flashcards

7 cards from real SCT 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. What DTC prefix indicates a generic (SAE-standardized) emissions-related powertrain fault in the OBD II system?

    Answer: P0 (Generic Powertrain)

    P0 codes are generic SAE-standardized powertrain diagnostic trouble codes, and most emissions-related faults are classified under this category.

  2. What does a 'pending' DTC in an OBD II system indicate?

    Answer: A fault detected once but not yet confirmed through a second drive cycle

    A pending DTC means the OBD II system detected a potential fault during one drive cycle but requires confirmation in a second drive cycle before setting a confirmed code and illuminating the MIL.

  3. What engine parameter does OBD II standard PID $05 (Mode 01, PID 05) report?

    Answer: Engine coolant temperature

    OBD II PID $05 reports engine coolant temperature, which is critical for verifying the engine has reached normal operating temperature before accurate emission tests can be performed.

  4. How many consecutive confirmed detections (drive cycles) does an OBD II system typically require before setting a confirmed DTC and illuminating the MIL?

    Answer: Two consecutive drive cycles

    Most OBD II monitors require a fault to be detected in two consecutive drive cycles before setting a confirmed DTC and illuminating the MIL, helping prevent false positives from transient conditions.

  5. What does the OBD II oxygen sensor monitor evaluate during its self-test?

    Answer: The response time and output voltage range of upstream and downstream O2 sensors

    The oxygen sensor monitor evaluates the switching frequency, response time, and voltage output of both upstream (pre-cat) and downstream (post-cat) O2 sensors to verify proper fuel control feedback.

  6. Which OBD II communication protocol became mandatory for all light-duty vehicles sold in the United States starting with model year 2008?

    Answer: ISO 15765-4 (CAN)

    ISO 15765-4 (Controller Area Network/CAN) became the mandatory OBD II communication protocol for all light-duty US vehicles beginning with model year 2008, replacing older protocols.

  7. What action must a smog technician take when a vehicle arrives for inspection with a flashing (blinking) MIL?

    Answer: Immediately fail the vehicle, as a flashing MIL indicates active catalyst-damaging misfires

    A flashing MIL indicates active severe misfires that can damage the catalytic converter; the vehicle must be immediately failed and the owner directed to seek repair before testing.