Motormouth: A new glitch in an older car is a reason for concern

Q: I have a 2011 GMC Sierra 1500 with 39,000 miles on it. Normally, the voltmeter shows just over 14 volts, but recently, after maybe a half-hour of driving, the reading starts to decline to about 12.75 volts. If I continue driving, it might or might not come back to 14 volts.

I tried a new alternator, and the battery was recently replaced. The GM dealer checked it out and said this was normal. I find this hard to believe. This didn't happen during the previous 10 years.

A: If this has cropped up after not occurring the previous 10 years, yes, there is a problem. The alternator delivers about 14.2 volts to keep the battery charged. A reading of 12.75 indicates only battery voltage. There could be a problem with the battery connections or the ground connection from the battery. A loose connection is possible but unlikely on a GM side post battery. The vehicle's gauge might be misbehaving, and connecting a voltmeter would reveal this. The new alternator might even the problem.

Q: I bought a 2021 Chevrolet Tahoe High County with the 3.0 turbo diesel engine in May. I have had a problem with the Check Engine light coming on.

It is back in the shop at the dealership for the fifth time since I bought it. Each time I pick it up after they supposedly solved the issue, the engine light will come back on within days. The last time it was in the shop, they replaced the diesel oxidation catalyst and two sensors.

It is currently back in the shop. They have GM engineers working on the car, and they seem clueless on why the engine light keeps coming on. Do you think it's a manufacturing defect that cannot be corrected?

A: When the shop scans for the code that sets off the Check Engine light, is it always the same code? If so, as a resident of Texas, you might be able to invoke the state's lemon law.

Q: We have a brand-new Honda CRV Hybrid. We've never had a car with a key fob before, and we were wondering if it's OK to leave the fob in the car when we park it in our garage. Does it affect the car in any way?

A: I suggest that everyone keep the key fob far enough away from their car that the doors will not unlock if they accidentally push the button.

On many cars, leaving the fob inside allows the car to continue to communicate with it. This can result in current draws that may weaken the battery. Besides, cars are easier to steal if the keys (or fobs) are left inside.