Q. I have read your column every week for many years and really enjoy it. I bought a new 2025 Acura RDX SH-AWD Advance and have owned it since November. It currently has only 2,400 mostly local miles on it. The EPA fuel economy estimates are 21 mpg city, 27 mpg highway, and 23 mpg combined, but I’m only getting 16 mpg using Shell 93-octane gasoline. Could you please explain what I might be doing wrong?
A. Most likely, nothing. With such low mileage, about 300 miles per month, and most of those miles consisting of short local trips, fuel economy will typically fall short of EPA estimates. Also, if you use the remote-start feature, remember that idling gets zero miles per gallon. I suspect that if you took a 500-mile road trip, your fuel economy would improve significantly. I have a small SUV, and although I drive it several times a week, most trips are less than five miles. As a result, fuel economy is in the teens. The same vehicle, when used for my former 50-mile commute each way, consistently returned 30 to 32 mpg. Acura recommends premium fuel for best performance, but using 93-octane gasoline instead of 91-octane fuel is unlikely to improve fuel economy. It simply costs more.
Q. I purchased a new GMC Sierra 1500 in 2017 with a 5.3-liter engine. It now has 52,283 miles on it. I’ve been hearing a lot about the AFM (Active Fuel Management) system, which switches the engine from eight cylinders to four cylinders to save fuel. Owners have reported problems with lifters and camshafts that can lead to engine failure. Some people have purchased AFM-disabling devices that keep the engine operating on all eight cylinders all the time. I’m wondering what causes these failures and whether General Motors is doing anything to address the problem and help its customers.
A. The issues typically begin at 70,000 miles or more, often with a ticking noise caused by a sticking valve lifter. Poor maintenance may contribute to the problem, but AFM failures have also occurred on well-maintained engines. GM has not officially admitted to a widespread defect, although there have been several class-action lawsuits related to AFM-equipped engines. Interestingly, GM appears to have moved away from AFM on some newer models. If this were my truck, I would consider using a bypass device. Readers have told me that the product from Range Technology is among the better options. I have seen other devices online for as little as $40, but the Range Technology product appears to be a more thoroughly engineered solution.
Q. What is the purpose of the low-fuel warning light? I say it is a warning that I will be running out of gas soon. My partner says it is simply a reminder to fill up.
A. Typically, when the low-fuel light comes on, you have enough fuel remaining to travel about 30 to 50 miles before running out, although the exact distance varies by vehicle. More important, the fuel pump is cooled and lubricated by the gasoline in the tank. Regularly driving with the low-fuel warning light illuminated can shorten the life of the fuel pump. So not a reminder to fill up, more of a warning you are going to run out of gas.
Q. When I turn the key in the ignition, I sometimes hear a grinding noise. The noise does not happen all the time, usually on the second or third start of the day. What does this mean?
A. Typically, that means the starter drive is worn out. The starter motor has a small gear that engages a larger gear, called the ring gear, on the engine’s flywheel or flexplate. The starter drive may simply be worn, but if the ring gear has also been damaged, the repair can become much more expensive. At this point, you should have a mechanic listen to the noise and determine whether the problem is limited to the starter or involves the ring gear as well. In most cases, the culprit is a faulty starter.
Q. My toy car, a 25-year-old Pontiac Firebird, has an odd problem. The front turn-signal bulbs were burned out, and the sockets were so rusty that I had to break the bulbs to remove them. I replaced the bulbs with standard incandescent bulbs, not LEDs, and installed new sockets. About a month later, the lights stopped working and the bulbs were actually broken. There was no sign of moisture, and charging-system voltage was 14.3 volts. What happened?
A. I would start by rechecking the sockets and wiring. The other possibility is vibration. If the bulb sockets are loose or the replacement sockets do not fit securely, excessive vibration can shorten bulb life or even cause the filaments to break. I would replace the bulbs with original-equipment-quality replacements from a company such as Sylvania or Philips and avoid inexpensive no-name bulbs. Also inspect the socket fit and mounting points to make sure nothing is allowing excessive vibration.
Q. My newly purchased 2012 Ram 1500 with the 5.7-liter Hemi V8 has a problem. Every three or four weeks, it sets a misfire code for cylinder No. 4 and turns on the check-engine light. I don’t do anything, and then it fixes itself. The truck runs fine. Where do I start?
A. At 14 years old, start with the basics. Inspect the spark plugs, ignition coil, and coil boot for cylinder No. 4. This engine uses 16 spark plugs, and because of the expense involved, it is possible they have not been changed in a very long time or perhaps never. If the ignition components look good, I would move on to the fuel injector. A sticking or malfunctioning No. 4 injector could certainly cause an intermittent misfire. A scan tool capable of viewing misfire history and fuel-trim data may also help pinpoint the problem.
Last updated on September 25, 2026 by AAA Staff
John Paul is AAA Northeast’s Car Doctor and a nationally recognized expert in automotive technology and repair regularly answering reader questions in columns published across the region. He began his career as an automotive technician and attained ASE master technician certification more than 40 years ago.
Do you have a car question? Email the Car Doctor for a personal reply: jpaul@aaanortheast.com.
