I have a 1997 ford thunderbird and the check engine light is on I have

[Liz]

tried the gas cap what is next? I have changed the gas cap first recommended and the light still comes on what can I try next.

 

[Dan B]

If the code said your fuel system presure test failed, and you've installed the correct gas cap, then there is probably an AIR leak (not a fuel leak) somewhere in the fuel system (tank, fuel line, fuel vapor canister in the engine compartment, etc).

Also, if you've overfilled the gas tank, some fuel will get into the vapor return line and cause a code to be set.

 

[Charlie]

Check for damaged lines going to evaporator canister and tank pressure sensor, if equipped.

 

[Sam]

a lot of things it could be even if you changed tires it will come on i have a 2006 blazer i changed tires and came on the same day.. checked the owner manual and it said changing tires will do it. but the dealer wants to charge to turn it off.