That is probably the pressure sensor. Modern enhanced Evap systems are pressurized including the tank. If there is a leak in the evap, the pressure drops in the tank and sets off the trouble light. G body gas tank are not designed to be pressurized or to be used with modern enhanced evap systems. Stock G bodies use older design non-pressurized / non-enhanced Evap systems. You probably can reprogram the PCM to delete the sensor, but it will make your setup emissions illegal if that is enforced in your area. Because of this, only the Erods that GM sells are legal to swap into older cars since they have a non-enhanced Evap kit and is not considered tampering while disabling a enhanced Evap on a used motor is.
