This problem occurred last evening as my daughter was driving home from work in her 2005 4WD Toyota Highlander. The check engine and VSC (Vehicle Stability Control) lights came on in traffic and the computer set a P0442 code (small leak in EVAP system).
Apparently this is very common code on older Toyota vehicles, and it seems to be the default code anytime there's vacuum or fuel vapor leak in the intake, fuel, and or EVAP system. Hence it's a pain to troubleshoot because it covers so much sub-system territory. The most common cause is a leaking fuel cap (either seal is bad, the plastic is cracked, or is not an OEM Toyota cap). Other causes could be the usual array of hoses, the purge solenoid, or the vapor canister underneath the right rear of the vehicle.
The cap looked good -- and the rubber seal was smooth. Hence I eliminated that possibility. The only other option is to thoroughly inspect the entire array of hoses and start looking for a culprit. A better solution is to smoke it with a machine --
I removed the air filter box and assembly and hooked up my DIY smoke machine and proceeded to smoke the intake first. At first I didn't see anything, but after adding a light bar -- I saw small whiffs of smoke coming from a hose on the top of the intake --
BTW -- this cheap HF light bar works like a charm. The extra light helped locate the source of the smoke.
Ironically, the hose in question is the same hose that attaches to the factory installed EVAP vent test fitting.
It had a very small crack about 1-1/2" long -- here it is after I took it off and spread it apart.
I installed a bulk piece of 5/16" fuel line hose in its place and secured it with two worm drive hose clamps.
Bottom line - the P0442 code covers a lot of territory, and in most cases it's just a simple hose or clamp that has gone bad on older vehicles. That said, finding the leak can take forever due to the many hoses, components, and connections in all the associated systems.
Per Toyota: A P0442 could indicate a leak in the following systems
Missing or loose fuel cap
Incorrect fuel filler cap used
Fuel filler cap remains open or fails to close
Foreign matter caught in fuel filler cap
EVAP canister or fuel tank leaks
EVAP system hose leaking
Fuel tank leaking
There is a full explanation and excellent diagrams of the system and the P0442 code, at the following link....
https://parts.olathetoyota.com/p0442-code-toyota