OBD II Code P0442 means Evaporative System Malfunction, Small Leak.
A very good source of information about it is found at this article in the RepairPal Encyclopedia here; http://repairpal.com/OBD-II-Code-P0442
This is an emissions problem and better left for the pro's to diagnose rather than just changing parts and hoping for the best... Diagnostic test requires advanced scan tools and an EVAP smoke tester...
Vehicle Application: 1997 Buick Lesabre Custom 3.8L
Customer Concern: Trouble code P0442.
1. Before starting, verify the customer did not leave the gas cap loose at any time. Also check to see if there is any rust or debris on the filler neck where the gas cap seals against.
2. Using a scanner, verify the fuel tank pressure sensor voltage reads about 1.5 volts with the gas cap loose. The voltage should be stable.
3. Check all Evaporative Emission Control System (EVAP) lines, seals and components for leaks.
4. Verify the purge solenoid allows vacuum to pass through when energized by a scanner. It should seal shut when de-energized.
5. Install a long hose on the vent solenoid. While commanding the vent solenoid on with a scanner, place the hose to your mouth and suck against the solenoid. The solenoid should be sealed shut when energized by the scanner.
6. Do this procedure with the vent solenoid several times. Vent solenoids often leak on an intermittent basis.
Leaking Evaporative Hose
Loose Gas Cap
Purge Control Valve
Defective Vent Control Solenoid
Tech Tips: Note: The purge solenoid is a normally closed solenoid. The vent solenoid is a normally open solenoid.
Diagnostic Codes: P0442
...interrupter (magnet) may become demagnetized and/or fall off of the camshaft gear causing the Check Engine Light (Service Engine Soon) light to illuminate. On higher mileage vehicles it would be advisable to...