Automotive Service Excellence (ASE) A8 Engine PerformanceFuel, Air Induction, and Exhaust Systems Diagnosis and RepairMedium
A technician is performing an evaporative emissions (EVAP) system diagnostic on a vehicle that recently had its fuel tank replaced. The system fails the leak test, and the technician suspects a component related to the recent repair. Which of the following components is MOST likely causing the EVAP system's failure?
- AA malfunctioning vent valve.
- BA disconnected or improperly sealed fuel tank pressure sensor hose.
- CA clogged charcoal canister.
- DA faulty purge valve.
Show answer & explanationAnswer & explanation
Correct answer: B. A disconnected or improperly sealed fuel tank pressure sensor hose.
When a fuel tank is replaced, components like the fuel tank pressure sensor and its associated hoses are often disconnected and reconnected. If the hose is disconnected or improperly sealed, it will create a leak in the EVAP system, causing it to fail a leak test. DTCs like P0455 (large leak) or P0442 (small leak) would likely set.
Why the other options are wrong
- A. A malfunctioning vent valve is not directly related to a fuel tank replacement, though it can cause EVAP issues.
- C. A clogged charcoal canister is typically not a direct consequence of a fuel tank replacement.
- D. A faulty purge valve is not directly related to a fuel tank replacement, though it can cause EVAP issues.
EVAP System Components (Tank)
EVAP system components directly mounted on or connected to the fuel tank include the fuel tank pressure sensor, rollover valve, and associated hoses, all critical for leak integrity.
- Fuel tank pressure sensor measures tank pressure.
- Rollover valve prevents fuel spillage.
- Hoses connect tank to rest of EVAP system.
Memory trick: After a tank swap, check the connections made to the tank itself.