Q: I have a 2005 Saturn Ion with 127,000 miles. It's in very good condition for its age. However, about a year ago, I was driving about 25 miles per hour when the power steering indicator warning light came on and the power steering stopped working. At exactly the same time the transmission dropped down to and remained in low gear, the check engine light came on, and when I pressed the brake pedal, there was a clicking sound.

After a short time, everything simultaneously went back to normal. The car was fine for a while. Then it happened again. Now it's been happening intermittently. I took it to my mechanic, who checked it for loose wires and connectors. He even disconnected and reconnected all the connectors at the car's computer but could find nothing. Do you have any thoughts?

A: My first thought is to challenge your statement that this car is in very good condition.

My next thought is that perhaps a failing sensor put your car into "limp home mode," which is designed to protect the catalytic converter. If the computer gets a reading that suggests that harm might be done to your very expensive catalytic converter, it reduces the engine's power dramatically, making it seem like you're in low gear.

But you've got so many things going on that I think your mechanic was on the right track to look for a systemic electrical issue. What we'd do in a case like this is something called a shake test. Basically, we grab every wire and connector we can find and shake it, hoping that we can reproduce the problem.

There are many things it could be: a corroded ground wire, bad ignition switch, dirty connectors in a wire harness, computer glitch. Even a failing fuel pump could cause some of these symptoms.

I know you can't go to your local Saturn dealer anymore (RIP), but you might try a Chevy dealer, which serviced these cars after Saturn folded. Maybe they'll recognize the collection of symptoms. If they can't help, it's likely time for a new car.

The A, B, C's of convertibles

Q: Your explanation of why there are no four-door convertibles (the lack of a structural B-pillar) was misleading. There have been four-door convertibles. Most of these vehicles had the rear doors, known as "suicide doors," attached to the C-pillar. The best-known four-door convertibles were the 1961-1969 Lincoln Continentals. Mercedes-Benz built one in 2007. Periodically you have referenced memory lapses in your column. I assume this response was one of those instances.

A: I don't recall having memory lapses, but I do remember that there have been four-door convertibles. Our reader was asking why there are none now. The primary reason is that they're structurally deficient. And with an increased focus on safety, structural rigidity is more important today than ever.

The best way to build rigidity into a four-door car is with three full-length pillars — A, B and C (front of the front doors, front of the back doors and rear of the back doors) — attached to a permanent, rigid roof that holds everything together. Convertibles have no full-length B pillar, weakening the structure of the car.

The joints can be reinforced. So it's not that it can't be done. It's that it is very hard, very expensive and often impractical to do. In fact, the 2007 S-Class Mercedes four-door convertible you mentioned was only a concept car. It was never produced.

Contact Car Talk via e-mail by visiting cartalk.com.