The P0442 code on your 2022 Toyota Highlander indicates the ECM has detected a small leak in the evaporative emission control system. The EVAP system is sealed, and even small leaks allow fuel vapors to escape to the atmosphere.
How EVAP Leaks Are Detected
The ECM performs leak tests by sealing the EVAP system and monitoring pressure changes. A small leak causes gradual pressure loss that the ECM can measure. P0442 specifically indicates a leak larger than 0.020 inches but smaller than a gross leak.
Highlander EVAP System
The 2022 Highlander offers 2.5L hybrid and 3.5L V6 options. Both use sealed EVAP systems with the fuel tank, vapor lines, charcoal canister, and valves. The system must maintain integrity for proper emission control.
Common Small Leak Sources
Gas cap seal degradation is the most common cause. Cracked or deteriorated EVAP hoses develop small leaks. Loose hose connections at the canister or tank allow vapor escape. The purge valve or vent valve may not seal completely. The canister itself can develop cracks.
Diagnostic Approach
Start by replacing the gas cap with a known good unit—the cheapest fix if that's the problem. Use a smoke machine to find leaks—smoke introduced to the system will escape at leak points. Inspect all EVAP hoses and connections. Check the charcoal canister for damage. Test purge and vent valves for proper sealing.