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Q: I've heard a lot recently about catalytic converter thefts. My Toyota dealership is advertising a shield for theft protection. What are your thoughts? Does this shield cut off access for car maintenance?

A: A catalytic converter shield does not prevent thieves from getting what they want. But it certainly slows them down. And speed is the name of the game for these thieves, so any obstacle sends them searching for an easier mark. As for the second issue, because the converter is not a maintenance item, routine service is not impacted.

Going by the book

Q: Nobody reads their manual unless they can't change the time on the clock twice a year. I have read our manuals religiously for years. Our vehicles have the oil minder accessible by touching buttons on the steering wheel. And in the manual, it clearly says to change your oil every year or less. The oil minder usually has shown the oil life being diminished at about 15,000 miles.

The conversations I have had with kids at the oil change places declaring I am voiding my warranty are a story for another day. No one at these places has been able to find a place in my manuals where it says to change the oil every 3,000 miles. Reading the manual is way more fun than a lot of novels, and it actually saves you money. Thanks for pointing that out.

A: Thank you for backing me up.

Ride quality varies

Q: I recently had my mechanic put new struts on my 2010 Toyota Matrix purchased used nearly two years ago with 80,000 miles. He put on Excel-G KYB struts. They took the edge off its rough ride, but after about four months, it seems to be riding like it was before. What gives?

A: The struts you had installed are the same as the original equipment that came on the vehicle from the factory. Sometimes motorists' perceptions of ride quality change. Sometimes there might be a product issue. KYB is customer-friendly, and you can e-mail your concerns to

Tire sizes should match

Q: Can having one tire of a different size than the other three cause the TPMS (tire pressure monitoring system) to malfunction, or at least show a malfunction? My mechanic hasn't been able to figure out why the light keeps coming on. The tires are all good, and the system seems to be working fine. This is the only other thing I can think of.

A: You didn't say what make and model car you have, but unmatched tires could be a problem. While most cars have tire pressure sensors mounted on their wheels, others rely on the ABS (antilock brake system) to report if any wheel is spinning faster or slower than the others. Unmatched tires report unequal rotational speeds, and that triggers the warning light.

Bob Weber is a writer, mechanic and ASE-certified Master Automobile Technician. His writing has appeared in automotive trade publications, Consumer Guide and Consumers Digest. Send automotive questions along with name and town to