I have a 2004 Lexus GX 470 and after a road-trip from San Fran and back to so cal I got a code reading p0451. After trying many attempts to fix it (replacing gas cap, replacing fuel pressure sensor, and inspecting the evap can, you nspecting fuel lines etc.) I have no idea what’s the reason behind it giving me the code. The new gas cap (oem) at times doesn’t seem to sit properly on the bore so I’m constantly fixing it to close right. Is there something I’m missing? Would the gas cap give me that code? Im only getting the p0451 code and nothing else.

 

A faulty gas cap seal is one of the culprits leading to this code, but there are others as we will:

Defective EVAP pressure sensor
Loose or missing fuel cap
Clogged fuel tank pressure relief valve
Broken, collapsed, or burned EVAP hoses/lines Cracked or broken charcoal canister

Ultimately this code relates to gasoline gas pressure calibration issues.

fixing the gas cap is the easiest fix, but if that’s not working, the other causes are a PITA to diagnose and fix.