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Is it a bad idea to disconnect a battery to clear a check engine light?
John Paul, AAA Northeast's Car Doctor, answers a question from a reader who wants a check engine light cleared.
Q. What do you think about disconnecting the negative side cable of a battery for 10 seconds on a 2017 Mazda CX-5? I want to reset the dash and get rid of the check engine light. Do all the other functions that the computer controls stay set?
A. Disconnecting the battery will clear the check engine light, but it will not fix the problem that turned on the light initially. Disconnecting the battery will typically clear memory items such as the radio presets, seat memory, and the clock. It would be better to scan the computer for fault codes, repair the issue, and then electronically clear the code. If the check engine light comes back on, you still have more work to do.
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Q. Years ago, I was involved in an accident because the oncoming driver had no lights on. Today’s cars have an auto setting on the light switch and the sensor activates the lights when dark enough. Unfortunately, I still see so many drivers not using this function and driving without lights. It’s obviously dangerous. I suspect that the instrument cluster lights are illuminated, maybe giving the driver a sense the lights are on. Would you know if AAA or other driver safety organizations are addressing this?
A. As a lead instructor for AAA’s Defensive Driver classes, I would remind students of this issue all the time. This is especially true if your household has more than one car and one does not have automatic headlights (as is the case in our household). I also try to occasionally address the issue in my Car Doctor columns. Too often people get fooled into thinking their headlights are on, but it is only the daytime running lights. Nearly every state has some variation of a law that requires headlights on one half hour after sunset until sunrise. This also includes during rain and when visibility is under 1,000 feet.
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Q. I own a 2020 Cadillac CT5 and it is a “Certified Pre-Owned” (CPO) vehicle. The car was used by the Cadillac Motor Company Northeast Zone Manager prior to my purchase. The car just hit 14,000 miles and I am truly pleased with the vehicle. The CPO runs out at the end of next month and I went ahead and purchased an extended warranty through the finance manager at a nearby dealership. I just read that you do not endorse the purchase of an extended warranty. Did I make a mistake?
A. No mistake. A car like yours with many high-tech features is a very good candidate for an extended warranty. The dealer/manufacturer’s and (self-promotion) AAA’s warranties are the only ones I would recommend. In my 40 years at AAA I have seen so many of the television and now internet warranty companies come and go. In many cases the consumer is left with nothing but an expensive piece of paper. You did the right thing.
Q. I had been using Invisible Glass and found that lately it wasn’t as effective as it used to be. You suggested another brand which I tried and found to be less effective than I would have liked. Today I tried Invisible Glass Glass Stripper. It says to use it to prepare your windshield for something else like Rain-X. It is a very mild abrasive mixture. I have to admit, it did a great job on both the inside and outside of my windshield. Now I don’t know if you are supposed to use it on the inside but I did. I’m hoping there are no bad reactions to its use both inside and out.
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A. I have not seen the Invisible Glass Glass Stripper product, but will look for it the next time I am at the store. No one is fussier than my wife when it comes to clean car windows. I typically use Sprayway window cleaner and recently discovered Scott Shop paper towels for glass. These heavy duty (and a bit pricey) paper towels do a nice job. When the windows are clean, I still go over them with a new microfiber towel.
Q. I wish to replace my six-year-old car battery (no problems yet, just age). Can I install a replacement myself without disturbing any electronics? Disconnect the negative terminal first then proceed with the positive. Just reverse the procedure installing a new replacement?
A. In most cars yes, you can install a new battery with no issues. Yes the clock, radio presets, and memory functions will need to be reset. Some vehicles have anti-theft radios, you will need a radio code. With some cars the computer will need to relearn a few basics. This is usually nothing more than the engine may start and stall a couple of times after the battery is installed. Some European cars will need the battery/charging system reset or registered. The car will run fine but the car needs to know it has a new battery. At AAA when we change a battery, we use a memory saver, just to eliminate issues.
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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 at johnfpaul.podbean.com.
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