How To

John Paul, AAA Northeast's Car Doctor, discusses safe ways to maintain computer memory while changing a car battery.

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Q. I just saw a reader’s question about keeping the car running while replacing a battery. Although I had this done on my car a few years ago without any issues, I sort of agree with you on this being a bad idea. What do you think about this: instead of the engine running, attach a trickle charger or some other sort of 12-volt device to the car to keep the computer settings. Still a bad idea?

A. Some of the trickle chargers use the battery to regulate voltage, so that may not work to maintain the vehicle’s electronics memory. Some advanced battery chargers have a “supply” mode that maintains a constant voltage to the vehicle’s electrical system while the battery is disconnected. Some portable jump starters include a specific 12-volt output mode designed for this purpose. At AAA, when we replace a battery, we typically use a full-size jump pack to maintain memory. We attach it to a ground terminal and the positive cable, insulate the connection, and then disconnect the battery. In a pinch, could you use a 12-volt cordless tool battery and jumper wires to maintain the computer memory? Yes. And just to reiterate, it is never a good idea to change/disconnect a car’s battery with the engine running. 

Q. My wife just purchased a 2026 Subaru Forester. The engine starts at 1,500 RPM and after a few minutes goes down to 650 RPM or so. I explained to her to let the idle drop before driving away, which she does not. Is she causing harm to the engine by driving off at the higher RPMs?

A. Is she causing harm to the engine? Probably not. The elevated idle speed during startup is normal and part of the engine’s cold-start strategy. The car should be good to drive once all the warning lights on the dash turn off, regardless of the idle speed. What I recommend with any car (new or old) is to avoid hard acceleration for the first few minutes to allow all the vital fluids to circulate.

Q. My son’s Land Rover Defender’s key became deactivated. My husband brought him the other key so he could drive his car. How do we get his key reactivated?

A. Keys rarely become deactivated on their own. They are electronically programmed, so unless someone was trying to reprogram the key or the vehicle, it is unlikely, but still possible. This can sometimes happen if the fob is left in the car for an extended time. To reactivate a smart key, the vehicle must be started using another activated smart key, or the vehicle must be unlocked and locked using the InControl Remote App. At the same time, it would be wise to check or replace the fob battery if it is more than a couple of years old.

Q. I have a 2011 Ram 1500 that is in need of front and rear brakes. Can you recommend a good brand of replacement pads and rotors, and what type of pads? Would you recommend ceramic or semi-metallic brake pads for my truck? Should I stay with factory parts or aftermarket? Aftermarket seems to be less expensive, but I want quality parts.

A. Factory parts are always a good way to go, but, as you pointed out, they are expensive. The original equipment brake pads have a list price of $182. A quality aftermarket brake pad is less than half that cost. As for brands, many shops are using Akebono brake parts. I have used PowerStop pads and rotors on my own vehicles and had good luck. Traditional names such as Wagner, Bosch, and Raybestos still make a good-quality brake part. As for semi-metallic or ceramic fiber, both are good. Ceramic pads are generally quieter and produce less dust, while semi-metallic pads tend to provide better heat dissipation and braking performance under heavy loads or towing.

Q. We want to fix up a 1998 Buick LeSabre that was inherited. There is an issue with the horn. It sometimes (unpredictably) remains on after I remove my hand. On occasion, it has activated without pressing it. What could be the issue, and if parts are needed, are they difficult to obtain?

A. There are three parts to the horn. The horn switch is integrated into the driver airbag module (part of the airbag cover), horn relay/wiring, and horn. A first “guess” is to replace the horn relay, which is located in the fuse box in the engine compartment. The horn relay is a standard part and easily sourced. The more difficult part will be the horn switch/pad. Looking online, the GM part has been discontinued. A used part from a salvage yard may be your only option. These horn pads have been known to distort over time and cause phantom horn activation.

John Paul is AAA Northeast’s Car Doctor. He has over 40 years of experience in the automotive business and is an ASE-certified master technician. E-mail your Car Doctor question to [email protected]. Listen to the Car Doctor Podcast on Apple Podcasts or other popular podcast sites.