Automotive Service Excellence (ASE) A8 Engine PerformanceFuel, Air Induction, and Exhaust Systems Diagnosis and RepairEasy
A technician is diagnosing a vehicle with a P0455 (EVAP System Leak Detected - Large Leak) DTC. After performing a smoke test, smoke is observed leaking from the top of the fuel tank near the fuel pump module. What is the MOST likely cause?
- AA loose or cracked fuel filler neck.
- BA cracked charcoal canister.
- CA damaged fuel pump module seal.
- DA faulty EVAP purge valve.
Show answer & explanationAnswer & explanation
Correct answer: C. A damaged fuel pump module seal.
A P0455 indicates a large leak in the EVAP system. If smoke is seen leaking from the top of the fuel tank near the fuel pump module, it strongly suggests a problem with the seal around the fuel pump module, which is a common leak point in the EVAP system.
Why the other options are wrong
- A. A loose or cracked fuel filler neck would cause a P0455, but the smoke would be visible near the filler neck, not the fuel pump module.
- B. A cracked charcoal canister would cause a P0455, but smoke would be observed exiting the canister itself, usually located away from the fuel tank.
- D. A faulty EVAP purge valve, if stuck open, would cause a rich condition or stalling, not a P0455. If it were leaking, smoke would typically be seen around the valve in the engine bay.
P0455 Large Leak Diagnosis
A P0455 (EVAP Large Leak) often points to a significant breach in the EVAP system, which can be identified by a smoke test. Common sites include the fuel cap, filler neck, or the fuel pump module seal.
- Indicates a large leak (e.g., >0.040' orifice equivalent).
- Smoke test is the primary diagnostic tool.
- Fuel pump module seal is a frequent failure point.
- Can also be caused by a missing or loose fuel cap.
Memory trick: Smoke points to the leak.