Automotive Service Excellence (ASE) A8 Engine PerformanceEmissions Control Systems Diagnosis and RepairEasy
A vehicle is being diagnosed for a 'Check Engine' light and a DTC P0455 (Evaporative Emission System Leak Detected, Gross Leak). After performing a smoke test, the technician observes smoke exiting from a crack in the charcoal canister. What is the MOST appropriate next step?
- AClear the DTCs and road test the vehicle.
- BReplace the charcoal canister and clear the DTCs.
- CReplace the fuel cap and re-test the system.
- DInspect the purge valve for proper operation.
Show answer & explanationAnswer & explanation
Correct answer: B. Replace the charcoal canister and clear the DTCs.
The smoke test directly identified a gross leak in the charcoal canister. Replacing the faulty component is the correct repair action.
Why the other options are wrong
- A. Clearing DTCs without fixing the underlying issue will result in the code returning.
- C. While a faulty fuel cap can cause P0455, the smoke test directly identified the canister as the source of the leak, making the cap an unlikely primary cause now.
- D. The purge valve's operation is not directly related to a physical crack in the charcoal canister causing a gross leak.
EVAP Gross Leak Diagnosis
Diagnosing a 'gross leak' in the EVAP system typically involves using a smoke machine to visually locate the source of the vapor leak.
- DTC P0455 indicates a gross leak.
- Smoke test is the primary diagnostic tool.
- Common leak sources include hoses, fuel cap, and canister.
Memory trick: Smoke test reveals the big crack, replace the part, no more hack!