Code P0442, engine vacuum and EVAP

Hi,

The code is specific to a "small leak" in the EVAP system. An engine vacuum leak wouldn't cause this. The most common cause of this code is a bad fuel cap, loose, or missing cap, leak in the evap canister, evap hose leaking, leaking fuel tank, and so on.

Basically, a vacuum is applied to the EVAP system to make sure it can hold pressure. Something is allowing the vacuum to drop and the PCM recognizes that as a leak.

Since a small leak is difficult to find, most times a tech will smoke test the system. Smoke is injected into the system at a very low pressure. If there is a leak, smoke will leak out and you should be able to see it.

Also, if you have a scan tool, you can follow the directions below to see if there is a leak.

Here is what I suggest. First, confirm the fuel cap is tight. Also, remove it and confirm there is no corrosion or rust when the seal seats. You can have the cap tested as well.

If it is good, I would recommend smoke testing it. That will likely require you to take it to someone simply because no one owns one other than a shop.

Let me know if any of this helps or if you have other questions.

Take care,

Joe

See pics below.