CEI Evaporative Emission Control Systems 3

Question 1

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

Accepted Answer

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

Answer

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.

Question 2

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

Accepted Answer

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

Answer

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.

Question 3

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

Accepted Answer

Fuel cap pressure tester

Answer

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.

Question 4

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

Accepted Answer

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

Answer

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.

Question 5

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

Accepted Answer

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

Answer

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.

CEI - Certified Emission Inspector Practice Test

CEI - Certified Emission Inspector Practice Test

CEI Evaporative Emission Control Systems 3