Of all the ways in which a vehicle can fail, all the things that can trigger a check-engine light, perhaps none are so infuriating as the “EVAP System Malfunction.” It just doesn’t seem fair that this system, this thing that your car doesn’t even need to run, should cause so much aggravation. But evaporative emissions — gasoline evaporating out of the fuel tank — are amazingly expensive things. Think about how fast a small puddle of gasoline will evaporate from a hot sidewalk, and you’ll have some idea of how much money is just floating away through your leaking EVAP system. Now, that really IS infuriating.

Step 1

Verify that the gas cap is firmly tightened onto the gas tank entry point. The EVAP system also monitors the gas tank, so an open gas cap can be the largest — and perhaps only — leak in the system. Leave the fuel filler door open after you tighten the cap.