Are you sure the fuel tank venbt valve has been plugged into the correct sensor. The plug for the knock sensor fits it too and will throw up this fault code if connected the wrong way round i.e. konck sensor in fuel tank vent valve plug. The only difference is the connector colour - the knock sensor being brown/red and fuel tank vent valve black. THIS IS VERY IMPORTANT AS THIS FAULT HAS DESTROYED A CALLY T ENGINE ON ONE CLUB CALIBRA MEMBERS CAR AND I THINK IT WAS WHAT KILLED MINE TOO (VAUXHALL PLUGGED IT IN THE WRONG WAY ROUND FOR ME ).