Q I accidentally backed my 2004 Buick LeSabre into a concrete curb on the passenger side. While driving home, I heard a loud "clunk-clunk-clunk" at every bump in the road. My local shop inspected the undercarriage, said the shocks were leaking and replaced them. The "clunk-clunk-clunk" is still there. I went to the dealership and they also said the shocks were bad and replaced them again. The "clunk-clunk-clunk" is still there. The car has only 77,000 miles on it. What should I do?

A Apparently, the shocks aren't the problem. Have the shop or dealer take a close look at the ball stud on the arms of the automatic level control sensor assembly. If one of the arms is bent slightly or the ball stud/pivot was damaged by the curb, it may be catching as the arm moves up and down with the suspension. The noise you describe also can be associated with a broken or worn sway bar link or damaged sway bar or bushing.

Q I own a '97 3-liter Ford Taurus with 112,000 miles. When I move forward from a stop, the car hesitates. The "service engine soon" light has been on for several months, and the code is P0430. Could a clogged catalytic converter be causing the acceleration problem? A shop replaced the converter with an aftermarket one. A few weeks later, the light came on again, and I started having acceleration problems again. I've had the car for 10 years, and I'd really like to know what the problem is before I bring it in again.

A Have the spark plugs ever been replaced? New plugs were due at 100,000 miles in normal service or 60,000 miles in severe service.

Since you've seen fault codes associated with the converter, the front oxygen sensor may be part of the problem. A scan tool can monitor its "switch" rate -- an older oxygen sensor may not be able to respond quickly enough to changes.

Anything that causes the engine to run too rich or too lean can create the hesitation you describe. Check for any type of vacuum leak, a faulty or contaminated mass airflow sensor, a leaky fuel injector or fuel pressure regulator or an exhaust leak upstream of the oxygen sensor. Even old, high-resistance spark plug wires can cause this symptom.

There are many possible causes, but make sure you start with the basics. Remember the KISS principle: Try the simple things first.

Q I drive a 2001 SS Camaro. While I'm driving it, the radio and power windows will stop working, but if I hit the top of the dash, they come back on. What's causing this?

A Most likely a poor connection at the body control module, mounted under the dash on the passenger side near the blower motor, or the power window control module, on top of the transmission tunnel under the center of the dash.

Q I have a problem with the air bag on my '96 Taurus. When I start the car, the air bag warning light blinks four times, pauses then blinks twice, pauses and blinks four times again. It does this cycle five times, then stays on solid. What does this mean, and can I fix it myself?

A There's a problem with one of the crash sensor circuits. A "24" code identifies low resistance in a crash sensor circuit, a "42" code indicates high resistance or an open circuit. You can check the wiring and connections to the sensors mounted on the right and left side of the radiator grill. The air bag system is deactivated while the warning light is on, so if you can't find and fix this yourself, take the car to a professional.