Automotive Service Excellence (ASE) A8 Engine PerformanceComputerized Engine Controls Diagnosis and RepairEasy
A technician is performing a diagnosis on a vehicle that has a P0442 DTC (Evaporative Emission System Leak Detected Small Leak). After performing a visual inspection and finding no obvious issues, the technician connects a smoke machine to the EVAP system. Where should the technician primarily focus their inspection for the smoke to locate the leak?
- AOn the intake manifold and throttle body gaskets.
- BAt the brake booster hose and PCV valve.
- CAround the fuel tank sending unit and fuel filler neck.
- DAt the exhaust manifold and catalytic converter connections.
Show answer & explanationAnswer & explanation
Correct answer: C. Around the fuel tank sending unit and fuel filler neck.
The P0442 DTC specifically indicates a small leak in the Evaporative Emission (EVAP) system. This system is designed to prevent fuel vapors from escaping into the atmosphere. The most common areas for leaks in the EVAP system are around the fuel tank (sending unit, filler neck, fuel pump module seal) and the associated hoses and canisters.
Why the other options are wrong
- A. Intake manifold and throttle body gaskets are part of the engine's intake system. Leaks here would cause vacuum leaks and lean conditions (P0171/P0174), not EVAP leaks.
- B. The brake booster hose and PCV valve are part of the engine's vacuum and crankcase ventilation systems, respectively, and are not directly part of the EVAP system.
- D. Exhaust system leaks would typically cause different DTCs (e.g., P0420, P0430) and would not be part of the EVAP system.
EVAP System Small Leak Diagnosis
The Evaporative Emission (EVAP) system captures fuel vapors and prevents their release. A P0442 DTC indicates a small leak, typically found by introducing smoke into the system and visually locating its escape point.
- Common leak areas: fuel cap, fuel filler neck, fuel pump/sending unit seal.
- Also hoses, canister, purge valve, vent valve.
- Smoke machine is the primary diagnostic tool.
- Small leaks (P0442) are harder to find than gross leaks (P0455).
Memory trick: EVAP leak, smoke's the key, tank and lines, where vapors flee.