My 1999 Olds Intrigue has been giving me a P0442 code for quite awhile with no performance problems. Auto Zone told me to try replacing the gas cap, which I did, & the code returned. I also had a code for the oxygen sensor, but that never came back after clearing the codes & replacing the cap. They told me I would probably need a "smoke test" to find the leak. Does anyone know what this is & does anyone have any ideas of things to check before I have the expense of a garage or dealership?

PO442 indicates a small leak in the EVAP system. Inspect the gasket and sealing surface around the gas cap & fill - I know its a new cap, but check it anyway. I have seen the plastic tether wrapped around the cap O-ring causing a leak. Also, visually check all the EVAP system hoses under the hood and under the car going back to the fuel tank. Check the EVAP service ports (look like A/C charge ports) for missing dust cap or damaged schrader valves. The smoke test introduces smoke into the EVAP system to help "smoke out" the leak. Check all components closely & I bet you will find a damaged/kinked hose or hose end.
Corky