Q: I got a code for my EVAP (P1457)

First, it is not the PCV. (positive crankcase ventilation) The PCV is there to relieve pressure and gases from the crankcase. The evaporative system keeps the fuel in the fuel tank from evaporating into the atmosphere. They are two separate systems.

This particular code simply states there is a problem with the evaporative emissions system. It doesn’t really point to any one thing wrong, such as a leak. Since this code is so generic, a total system test will need to be run. This can only be done with a shop level scanner and a technician with the experience to understand the results. Evaporative system tests will activate all the valves and solenoids in the system in a fashion that will reveal what to look for. It could be a leak, a solenoid that is not working or a sensor that is reading incorrectly. There are pressure sensors on the fuel tank that are used by the system to check for leaks. This is done by using the vacuum in the engine to put the fuel tank into low pressure. If the tank does not hold this low pressure condition, a code will be set. This is a simplified version of the test. If the sensor is showing an incorrect value, the system will assume there is something wrong.

If it is a leak that needs to be chased, the most common place for leaks in an evaporative system, are the seals that seal the hose connections. When these seal dry, they contract and begin to leak. The best way to look for any leak in an evap system is through the use of a smoke machine. Unfortunately, smoke machines are expensive. It creates pressure in the evap system and injects smoke into it as well. Smoke will escape out any leak in the system.

Because of the tools involved and the complicated nature of evaporative emissions systems, I recommend the following inspection to help you out. Check engine light is on inspection

Good luck!