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Q: Are jumper packs a good investment? The idea of jumping your car battery without having to find someone to help is very appealing, especially if you are on your own. Prices vary widely. Any thoughts or recommendations?

A: About the size of a small loaf of bread, those battery packs can be lifesavers. Also known as battery banks or power banks, they not only can jump-start a car, but recharge your smartphone and other devices. Look for one with a capacity of about 10,000 mAh and peak output of about 1,000 amps. Like anything, you get what you pay for, but you can find many good units for under $100.

Stick to sticker

Q: A new car comes with tires. There are recommended air pressure measurements inscribed on the inside of the driver door. When a set of tires are bought to replace the originals, does one fill the tires to the pressures listed on the new tires or the door?

A: The sticker on the door lists the proper pressure no matter what may be molded into the tires' sidewalls. The pressure listed on the tires is its maximum safe inflation pressure, not the pressure to which you should inflate them.

EVAP problem

Q: My 2011 Toyota RAV4 with 95,000 miles has the "check engine" sensor and flashing "auto LSD" sensor on simultaneously. The situation began shortly after I encountered heavy rain on an interstate highway. Auto Zone performed a courtesy computer test and the report indicated two possible causes, both involving the EVAP system: either the vapor canister needs replacing or the leak detection pump is stuck "off." Someone suggested water might have entered that system and I should use a "dry gas" product, but that has not resolved the problem. Can you offer any advice?

A: It is uncommon for water to enter the vapor canister, but I am not saying it's impossible. The most common cause is overfilling the gas tank, which forces liquid gasoline into the canister that is designed to hold fuel vapors. Nevertheless, you might have to replace the canister, the pump or both.

Signal switch

Q: Back in 1987, I had an Oldsmobile Cutlass that had a standard safety feature that when the directionals were left on, chimes would sound. I haven't seen another vehicle with this feature since. Shouldn't this be standard in every vehicle?

A: This would be a fabulous feature. I can't tell you how many times I have followed someone at an extended distance expecting them to turn. More often than not, they make a lane change in the other direction. In my opinion, even better than a chime would be timed, self-canceling turn signals. My Harley has had this feature for many years.

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