ASE4 OBD II and Scan Tool Diagnostics 2

Question 1

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

Accepted Answer

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

Answer

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.

Question 2

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

Accepted Answer

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

Answer

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.

Question 3

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

Accepted Answer

Engine RPM calculated from the crankshaft position sensor

Answer

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

Question 4

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

Accepted Answer

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

Answer

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.

Question 5

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

Accepted Answer

To store learned baseline fuel corrections that persist across ignition cycles

Answer

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.

ASE4 - ASE Automobile Engine Performance Practice Test

ASE4 - ASE Automobile Engine Performance Practice Test

ASE4 OBD II and Scan Tool Diagnostics 2