Code gm po442 - 1998 Buick LeSabre

po121 is throttle position sensor is out of range.po442 is emissions system leak detected small leak.po455 is same as po442 but large leak.po496 is high purge flow . Check all the vacuum lines plastic also cause one of them is broken.

Google the codes & read up

You need a repair shop to diagnose
the Evap System

TYPE: OBD PO442

Just fixed mine with the same code and gm tech advised me to change thermostat which is not a fun job as it is located in the LOWER hose and comes with a gooseneck assembly and O ring.The temp sensor could also be the problem but was told not likely so got by with just thermostat!

CODE PO442 EVAP SYSTEM SMALL LEAK DETECTED CONDITIONS.POSSIBLE CAUSE- LOOSE OR DAMAGED GAS CAP-FUEL TANK PRESSURE SENSOR IS DAMAGED-.FUEL TANK VAPOR LINE LINES IS CLOGGED OR DAMAGED DISCONNECTED-.PURGE VAPOR LINE IS CLOGGED DAMAGED DISCONNECTED.-PURGE SOLENOID OR VENT SOLENOID HAS A SMALL LEAKING STICKING - PCM HAS FAILED.

po442= evap emission control system leak (small)
po742= torque converter clutch soleniod circuit stuck on
i got these out of the booklet for my code reader po442pd wasn't listed

There is a pretty good emissions leak somewhere.

you have a small leak in your evap system

EVAP Codes. You will have to go thru entire evap system,looking for a small leak (po442) Hoses,Switches,Valves etc. See if you can borrow a smoke machine.

THESE ARE FROM THE GM CODE DEFINITION MANUAL

P0135 - Heated Oxygen Sensor (HO2S) Heater Performance Bank 1 Sensor 1
P0449 - Evaporative Emission (EVAP) Vent Solenoid Control Circuit
P0442 - Evaporative Emission (EVAP) System Small Leak Detected

PO442 is an Evaporation Emission leak. It's probably a loose gas cap. The fix would be $96.00 at our dealership, since your truck is out of warranty. You may be able to get it fixed cheaper, but you'll be charged a diagnostic fee.