Brand: Saturn runs fine, but 'Check engine' light stays on

Q: I own a 2005 Saturn Ion with the 2.2-liter engine. At approximately 90,000 miles the "Check gas cap" warning light came on, which shortly thereafter triggered the "Check engine" warning light. I have checked and cleaned everything, bought an aftermarket cap which was of no help, installed a new GM factory gas cap — none of which helped. I've disconnected the battery numerous times to allow it to reset but the light continues to come on. I've checked online and find that hundreds of Saturn owners have the same complaint and have spent a lot of time and money having diagnostic work done at their dealerships and shops, to no avail. The car runs fine with no problems other than that glaring yellow "Check engine light" that I've finally just left on. Can you help?

A: Have you ever had a scan tool indentify the DTC fault code that is triggering the light? I found service bulletin #PIT4943C in my ALLDATA database dated February 2014 that focuses on small EVAP leak diagnosis. For example, DTC P0442 will set when the fuel pressure sensor in the fuel tank indicates a smaller than predicted vapor pressure change in the tank after the engine is shut down.

I know this sounds somewhat backwards, but the tank will show a vapor pressure change as the fuel cools down upon engine shutdown. If there's a a vacuum or pressure leak in the EVAP system, the pressure change will be less because there's less pressure at shutdown due to the leak.

The bulletin outlines a specific series of tests utilizing the GM scan tool and non-toxic smoke to pinpoint any EVAP leak. Suspects include the purge solenoid, gas cap, canister vent solenoid or any air leaks in the EVAP system's quick-disconnect fittings.

Q: I have a sports car that I drive from April to November. Should I change the oil before storage or wait until the spring when I start driving it? I hear some folks say store with clean oil and some say change in the spring because of water accumulated in the oil of stored vehicles.

A: I've always chosen to change oil just prior to "long-term parking" over the winter. Doing so removes any soluble contaminants from the engine. As for moisture/water condensing in the lubricant, please note that as long as the engine does not experience rapid temperature changes, condensation won't be significant.

If you choose to not start the engine during its winter "nap," don't worry about condensation. If you do choose to start the engine periodically, make sure you allow it to fully warm up and run long enough to evaporate any condensation that may occur.

Q: I am getting to the age where I can afford to get a fun car for a change. I'm thinking of a late-model Corvette. Here is my question: Why don't Corvette owners drive their cars in winter? Is it because the ride is so low that they tend to get stuck in even modest snowfalls? The owners are protecting their investment from winter-assisted rust? The traction in snow is very poor? If a person owns a Corvette, they can afford to winter in Boca Raton, Fla., and leave the car in their Minnesota garage.

A: The answer to all your questions is "yes" — poor traction, low ride height and vulnerability. Have you ever seen what happens to cold fiberglass in a crash? It doesn't just crack, it shatters like glass. Rust isn't as big an issue because newer Corvettes feature aluminum chassis and suspension components, but there's still lots of steel under the chassis.

A better idea would be to drive the Corvette to Florida for the winter so you can continue to enjoy it year-round!

Paul Brand is the author of "How to Repair Your Car" and "How to Repair Your Truck and SUV," published by Motorbooks.