Dear Tom and Ray:

My wife and I purchased a 2013 Prius in July 2013. We were parked at a mall when we had an unusual problem: I started the car and the "check hybrid system" light came on. We called Toyota's 800 number to have our car towed to the nearest Toyota dealership. The people at the dealership "powered down" the system, then "booted it up" again, and we drove home. About a week later, the same thing happened. We had it towed to the nearest Toyota dealership, and we got our car back about a week later. I was told that the electronics in the car may have "a loose connection." When I went to start the car, the problem recurred.

Another week passed and I got a call that my car was ready. The mechanic told me they replaced one defective computer cell, and the computer was "talking to itself." I went into the parking lot to start the car, and the XM radio was knocked out. After two and a half hours of waiting (again) for them to repair the XM, I was told by the mechanic that the car got stuck in reverse when it came off the lift and that the rear camera was not functioning. To make a long story short, Toyota replaced our Toyota 2013 Prius with a 2014 Prius. My question is (you were wondering when I'd ask it): How complicated are the electronics in a hybrid like the Prius? Can one thing going wrong cause a whole series of problems?

-- Joseph

RAY: They're very complicated.

TOM: Most people know that engine management has become computerized over the past couple of decades, with the computer figuring out how much air and fuel to send into the cylinders and controlling for emissions.

RAY: But not everyone realizes that almost everything else is now computerized, too: Shifting, braking, handling, safety systems, lighting, even steering and accelerator inputs are now being done "by wire."

TOM: So cars now have not just one, but many computers. And while that has a huge number of benefits, it also increases the complexity.

RAY: To all of that, the Prius adds a computer to manage its hybrid propulsion system. It decides when to use the electric motor to power the wheels, when to switch to the gasoline engine, and when to combine the two. It manages the regenerative braking system and the level of charge in the hybrid battery.

TOM: So the Prius is the poster child for electronic complexity in cars. But I'm not sure any of that explains why your car was so unreliable. I'm guessing your car was suffering from a fatal case of F.O.T.: fell off truck.

RAY: I think someone forgot to secure it to a car carrier or a lift, and ... kersplat. Hey, my brother's done it!

TOM: When there are electrical gremlins on a new car and even replacing the computers doesn't make them go away, you have to suspect an accident, where some unseen wiring got partially severed or pinched.

RAY: The problem could be hidden inside the wiring sheath, which makes it very hard to find, especially when the problem shows up only intermittently.

TOM: Toyota finally did the right thing for you by raising the white flag and giving you a brand-new car. Good for them.

RAY: Based on what we see in our own shop, your problems were highly unusual. We've never seen problems like this on a Prius, so I'm guessing you had a one-of-a-kind. You lucky devil!

TOM: So as long as the 2014 didn't fall off the delivery truck, you shouldn't have to worry about this again, Joseph -- complexity or not. Good luck.