Automotive Service Excellence (ASE) A8 Engine PerformanceFuel, Air Induction, and Exhaust Systems Diagnosis and RepairMedium
A technician is performing a diagnostic on a vehicle that intermittently stalls after refueling. The fuel tank is full. Which component of the EVAP system is MOST likely to be at fault?
- AA restricted charcoal canister.
- BA leaking fuel tank cap.
- CA faulty purge valve.
- DA malfunctioning fuel tank pressure sensor.
Show answer & explanationAnswer & explanation
Correct answer: C. A faulty purge valve.
If the purge valve sticks open, it allows fuel vapors from the charcoal canister to be drawn into the engine at an uncontrolled rate, typically causing a rich condition, rough idle, or stalling, especially after refueling when the canister is saturated with vapors.
Why the other options are wrong
- A. A restricted charcoal canister would prevent proper venting or purging, potentially leading to tank pressure issues or P0440/P0442/P0446 codes, but not typically stalling after refueling.
- B. A leaking fuel tank cap would cause an EVAP leak (P0442/P0455) and prevent the system from sealing, but not directly cause stalling after refueling.
- D. A malfunctioning fuel tank pressure sensor might cause EVAP codes or incorrect gauge readings, but it wouldn't directly cause stalling by changing the fuel-air mixture.
Stuck Open Purge Valve
A purge valve stuck open allows excessive fuel vapors into the engine, leading to an overly rich mixture, rough idle, or stalling, especially after refueling.
- Causes rich condition.
- Symptoms often appear after refueling.
- Can cause P0172 (system too rich) DTCs.
- Can be tested with a scan tool or vacuum gauge.
Memory trick: Stall after fill, purge valve spill.