Q: My 2014 Jeep Grand Cherokee suddenly developed a clunk downshifting at a stop sign. Then, at the next stop sign, even my wife heard it. I took it to my regular garage, which I have great trust in. They used a machine to analyze it, and they fixed the clunk. In looking at the invoice, there was the labor charge: reprogram PCM/TCM for $175. Not in an upset mode, I simply inquired as to what is a "reprogram PCM/TCM $175." The service manager stammered as if he was unable to answer. The implication I got was that he was not sure what the machine does, but it simply fixes the clunk. Which it did! Can you give me a better idea of what happened?

A: Have you ever downloaded an update for one of your phone's apps? You are quite able to use it without knowing how the app works. In the case of the Jeep, your mechanic downloaded updates for both the powertrain control module (PCM) and the transmission control module (TCM). He knew what to do without needing to know what the update modified.

Price watching

Q: When electric vehicles become more commonplace than cars powered by gasoline, do you think that the cost of electricity will fluctuate the way that gasoline prices do? Would it affect the home electricity bill beyond the vehicles' share of consumption?

A: Electricity prices are controlled by state utilities agencies. To increase prices, power providers usually must petition the agency for permission. Fortunately, electricity fluctuations are limited to only occasional brownouts.

Lighting the way

Q: I have a 2003 Chevy Trailblazer with 138,000 miles. I always have set the headlights so they always are on, and I have burned out two or three modules over the years as well as a few headlights. Should I just put the lights on when I drive at night or in the rain?

A: Having the headlights on all the time increases your visibility to other drivers and, therefore, enhances your safety. However, other than during rain, when many states (including Minnesota) require you to have your headlights on, the daytime running lights are adequate for this.

Before and after

Q: I know I should wax my car twice a year, but I don't. That being said, and leaving my car outside of the garage all year, would it be better to wax before summer's hot sun or the snow, ice and freezing temperatures of winter? Or should I wait until after those seasons?

A: I'm in the "before" camp, but saying "before summer" is the same as saying "after winter," and vice versa. Wax your car in the spring and fall when the weather is more favorable for doing the job. Whether you think of that as "before" or "after" is up to you.

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 motormouth.tribune@gmail.com.