When to change my fuel cap?

first of all if you use silicone sealer it will not hold for fuel. the gas breaks it down. if you have a code for an exap system leal then you need to take it to a repair shop that can smoke test the system for leaks

2006 Equinox large leak check Engine Light P0440 (possible solution): We got a P0440 code with the large leak (emissions). We found we had to purchase a CERTAIN TYPE OF GAS CAP. We had to get a NON-VENTED or VACUUM locking gas cap. We kept getting a check engine light for months. We have a 2006 Equinox and purchased a STANT #10511 NON-VENTED OR VACUUM locking gas cap for an 2006 Equinox - Guess what? NO CHECK ENGINE LIGHT! Walmart and Advance Auto sales them: https://www.walmart.com/ip/STANT-10511-Fuel-Cap-Locking-1-9-16-in.-Dia.-G9510444/44960112#about-item STANT 10511 Fuel Cap, Locking, 1-9/16 in. Dia. Fuel Cap, Nonvented, Locking, Thread Type: Quick-on, Cap Dia. 1-9/16 In., Material Plastic Most auto stores sale vented gas caps which prevents pressure in the system but we have found our 2006 Equinox uses pressure to detect a leak in the emissions system. So far no more check engine light! Hope this helps!