This code means you have a small evaporative system leak. It will be
difficult to find with the naked eye and will be nearly impossible to
diagnose efficiently without the scan tool.
Here's my opinion on the top causes of this code, in order:
1. Improperly installed fuel cap (not tight, crossthreaded, tether under
2. Canister close valve which does not fully seal.
3. All other causes combined (too many to list). Basically, this would
be any other type of vapor leakage.
You can check the fuel cap sealing ring and the filler neck for a smooth
sealing surface. In this case, the problem will not be the purge valve.
The system tests itself by vacuuming the tank with engine vacuum by way of
the purge valve. The code P0442 indicates the vacuum in the system bleeds
off after the system is sealed. If the purge valve were leaking, the
system would have more vacuum, not less.
Hope all that helps. You may wind up having to let the dealer look at