Dear Doctor: I own a 2003 Chrysler PT Cruiser with only 36,000 miles. The "check engine" light comes on intermittently with the code P0441. I replaced the purge solenoid and that eliminated the code for a while. When it came back again I replaced the forward oxygen sensor. That solved the problem for a few months but now it has returned. Do you have other suggestions? -- Steve

Dear Steve: The P0441 code is EVAP evaporative emission-related and is not the oxygen sensors. The EVAP system is the ventilation system of the fuel tank. The code indicates a small air leak in the system. It could be as simple as a poor gas cap seal (always use a factory non-locking cap). Leak detection pumps are also a common problem.

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Dear Doctor: I own a 1989 Pontiac Trans Am with just 13,500 miles. Lately, my battery has been going dead (even the new one I purchased). I believe it's because the two cooling fans have been starting and running for short periods of time at intervals when they are not supposed to activate. I think their only purpose is to accelerate the engine cooling after the engine is turned off. My dealer says the thermostat is fine and they are stumped. I've also heard the fans kick on for no apparent reason. Do you have any suggestions? -- Lawrence

Dear Lawrence: You have a rare car with very low miles. You did not mention how long the car sits before the battery goes dead. For the cooling fans to be the problem they would have to run for an hour-plus. The technician will have to connect a digital volt amp meter in series and check the parasitic drain. There should be no more that 60 mili amp current draw. You can install a battery cut-off switch, or battery low voltage shut-off electronic switch. Current draw on some computer-controlled vehicles will kill batteries in less than 60 days.

Dear Doctor: Some of my school students are claiming that when they sit in the front passenger seat of their parent's car once they put on their seat belt, the airbag light goes on. Is it the person's weight or is there a malfunction with the seat belts or airbags? -- Carl

Dear Carl: The vehicle's airbag system uses the weight of a person to energize (arm) the airbags in the seat occupied. Airbag technology has come a long way over the years, both in sensors for deployment and the force they deploy.

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Dear Doctor: Have you test-driven the 2014 Chevy Silverado? Can you tell me what's new about it? -- Dave

Dear Dave: I drove the 2014 Silverado LT Crew Cab 5.3-liter V-8 with the 6-speed automatic 2WD. What's new are triple-sealing in the doors, combined with redesigned mirrors, making for a very quiet interior. The tailgate is now spring-loaded and the rear bumper has small steps on either side, along with built-in grab handles in the rear section of the bed. The electric power steering has quick response and great road feel. Base price of the LT is $35,855.

Dear Doctor: I'm interested in buying a used Jeep Wrangler Unlimited. Some time ago you reported on the improvements made on the Unlimited over the years. What are they? I would also like to know your thoughts on the Jeep Liberty. I value your recommendations. --Ken

Dear Ken: I personally own a Wrangler automatic six-cylinder with conventional smooth summer tire tread pattern. The Wrangler Unlimited has a longer wheelbase and is much roomier than the standard Wrangler. It has a smoother ride because of the longer wheelbase. I service a lot of Wrangler and Liberty Jeeps. There were some problems with a small number engine head gaskets (most covered under warranty). With the Wrangler the top comes off, so it's a whole different feeling when driving. The Liberty will offer a quieter ride. These are two distinct vehicles. I would suggest which ever Jeep you buy to go with an automatic transmission. -- Junior Damato, Motor Matters

Junior Damato is an ASE-certified Master Technician. Email questions to Mail questions to: Motor Matters, PO Box 3305, Wilmington, DE 19804