Diagnostic Aids

When diagnosing intermittent problem, use scan tool to review malfunction history diagnostic information. Using scan tool, perform EVAP SERVICE BAY TEST. This verifies large leak is present. If diagnostic passes, it may necessary to review the importance of a tight, secure fuel cap with vehicle owner.

Possible causes of a large leak:

Fuel cap missing, incorrectly installed or leaking.
EVAP vent solenoid stuck open.
EVAP purge solenoid stuck closed or blocked.
EVAP vent hose loose or damaged.
EVAP canister damaged.
Fuel sender assembly "O" ring leaking.
Fuel tank or filler neck leaking.

NOTE: A very large leak, such as a missing fuel cap, may be difficult to pick up with ultrasonic leak detector.