Q We drive a 2001 Dodge Ram with the 5.8-liter engine and 100,000 miles. Three weeks ago we noticed a red icon on the dash, which at first we did not recognize as a "check engine" light. Two weeks later an "air bag" icon came on and we realized the first light was the check-engine warning. A mechanic told us that because we'd been driving without problems for so long with the warning lights on that we probably had a weak sensor on the engine and something wrong in the steering column. What should we do?

A The mechanic may well be correct. Have a shop connect a diagnostic scan tool to the vehicle's diagnostic link and read the specific fault codes that have triggered both warning lights. Since the vehicle apparently continues to run well, the "check engine" light may well be a sluggish oxygen sensor due to age and mileage. If so, it's worth replacing in order to restore fuel mileage and performance.

The more important issue at the moment is the "air bag" warning light, which indicates that the air bags are disabled. The most common failure due to age and mileage is the clockspring mechanism that electrically connects the air bag in the rotating steering wheel to the harness in the steering column.

Researching through my Alldata automotive database, I find that Chrysler issued a recall in June 2001 involving the clockspring on certain 2000-2001 Ram trucks. Check with your dealer to find out if your vehicle was included in this recall. Regardless of whether it's covered by a recall, for your safety in the event of a serious crash, have the air bag system repaired.

Q I read money-saving tips telling us not to use premium gas, and that 87 octane will perform just as well. However, some vehicles such as BMW, Infiniti, Lexus and others call for premium fuel. Would using other than premium void the warranty? Will it hurt the engine?

A Many modern engine management systems use a "knock sensor" -- literally a small microphone -- that listens for the characteristic "ping/knock" sounds of pre-ignition or detonation. Based on the signal from the knock sensor, the engine control module (ECM) can adjust fuel mixture and ignition timing to eliminate this. I don't think you'll damage your engine by using lower-octane fuel, so I don't think there would be a warranty issue.

On the other hand, running significantly lower-octane fuel could hurt fuel mileage and performance for the simple reason that the feedback from the knock sensor may force the ECM to de-tune the engine to operate on this fuel.

To keep it simple, run your vehicle on the lowest-octane fuel it will operate properly on. Higher-than-necessary octane is a waste of money and offers no mileage or performance benefits.

Q After an oil change, the sticker placed on my windshield calls for the next oil change in three months or 3,000 miles. I drive my van less than 6,000 miles a year. Is it necessary to have an oil change after three months if the vehicle is still nowhere near the 3,000-mile recommendation?

A In my opinion, no. Modern engine technology and better lubricants allow car makers to recommend oil changes at much longer intervals. My personal guideline is 4,000 to 5,000 miles regardless of time.