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OBD II and Scan Tool Diagnostics Flashcards

7 cards from real ASE4 practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 OBD II and Scan Tool Diagnostics flashcards as text

  1. What type of information does OBD II Mode $06 provide to a technician?

    Answer: On-board monitoring test results showing actual values versus pass/fail thresholds

    Mode $06 reports the results of non-continuously monitored system tests, displaying actual measured values alongside minimum and maximum thresholds — useful for identifying borderline failures before a DTC sets.

  2. A 'pending' DTC stored in Mode $07 means:

    Answer: A fault was detected on one trip but has not yet been confirmed on a second trip

    A pending DTC indicates the OBD II system detected a fault during one trip but requires a second trip confirmation before illuminating the MIL, based on the two-trip detection strategy.

  3. On a scan tool, OBD II Mode $01 PID $0C displays which parameter?

    Answer: Engine RPM calculated from the crankshaft position sensor

    PID $0C in Mode $01 (current data) reports calculated engine RPM derived from the crankshaft position sensor signal frequency.

  4. A short-term fuel trim (STFT) reading of +15% indicates the ECM is:

    Answer: Adding fuel to compensate for a lean condition detected by the O2 sensor

    A positive STFT means the ECM is commanding more fuel (15% above the base fueling map) in real-time response to an oxygen sensor indicating a lean exhaust condition.

  5. What is the primary function of long-term fuel trim (LTFT) stored in the ECM?

    Answer: To store learned baseline fuel corrections that persist across ignition cycles

    LTFT stores accumulated fuel delivery corrections in non-volatile ECM memory, compensating long-term for changes such as injector wear, vacuum leaks, sensor drift, or fuel pressure variations.

  6. If both STFT and LTFT are consistently at -15% across all load conditions, the most likely cause is:

    Answer: Excessive fuel delivery from high fuel pressure or leaking injectors

    Consistently negative fuel trims indicate a persistent rich condition — the ECM is reducing fuel significantly, pointing to causes such as excessive fuel pressure, leaking injectors, or a purged evaporative canister flooding the intake.

  7. Which pin of the OBD II DLC (Data Link Connector) provides unswitched battery voltage to power the scan tool?

    Answer: Pin 16

    Pin 16 of the standardized 16-pin OBD II DLC provides constant (unswitched) battery power so the scan tool remains powered regardless of ignition switch position.