A GMC trouble code of P0466 gives the mechanic or owner a couple of ideas as to the cause of the code. The P0466 is a generic code, one of the many on-board diagnostics (OBD)-II codes available.
The code it itself can give you an idea of where the engine problem might be. For the P0466, the 'P' stands for powertrain. The second digit, '0,' means it is generic, and not manufacturer-specific. The third digit, '4,' is equal to the emission control system of the vehicle. The last two digits are variable and refer to a particular problem. In this case it is a purge flow sensor circuit range/performance issue.
One possibility for the computer issuing this code is a loose gas cap. This could be from the gas cap not being put back on correctly to the gas cap being faulty and in need of replacement. When the fuel tank is pressurized during normal operation, the pressure leaks out and causes the computer to issue this code.
The second cause for this code is a faulty evaporative purge flow sensor. The evaporative purge flow sensor lets the car's computer know how much fuel vapor is returned to the engine for reburning. This is an issue best left to trained technicians to fix.
