The P0442 code indicates that the engine control module has detected a small leak in the evaporative emission (EVAP) system. This system is designed to prevent gasoline vapors from escaping the fuel tank and entering the atmosphere.
A loose, damaged, or incorrect gas cap seal is the most common cause of a small EVAP leak.
Rubber hoses in the EVAP system can develop small cracks, dry rot, or become disconnected over time.
A vent valve that does not seal completely allows air to enter the system, triggering a leak detection.
A purge valve that fails to close fully can allow the system to lose pressure or vacuum.
The canister housing may develop small cracks or leaks due to physical damage or age.
Internal failure of the engine computer is highly unlikely but could theoretically cause a false leak detection.
The definition is universal; the diagnostics are engine-specific. Open your vehicle for the codes documented for it:
Yes, the gas cap is the primary seal for the EVAP system; if it is loose or the gasket is worn, the system cannot maintain the required pressure.
No, P0442 is an emissions-related code and does not typically affect the drivability or mechanical performance of the engine.
No. It is extremely rare for the PCM to cause a P0442. Small leaks are often difficult to find, and a thorough smoke test is the appropriate solution rather than replacing the computer.