Q My sister has a 2003 Toyota Highlander with 60,000 miles on it, and she has always taken it to the local dealer for service. Recently, the check-engine light came on. The evaporative emissions system's charcoal canister has a crack in it, causing it to leak fuel vapor. The dealer says replacing it will cost $700.

Doesn't this fall under the federal emission warranty? I did read that every emission part is covered for the first two years or 24,000 miles, but could they make an exception in a case like this? Could I seek help from the attorney general's office?

A The federal emissions warranty covering 1995 and later vehicles includes a "performance warranty" that covers emission components that cause the vehicle to fail a state emissions test for two years or 24,000 miles, and a "design and defect warranty" that also covers "major specified emissions control components" for eight years or 80,000 miles. These "major specified" components are the catalytic converters and engine management computers, but not the charcoal canister.

You could try locating a replacement in a salvage yard at a fraction of that cost. At U-Pull-R-Parts, a charcoal canister is $9.

Q My wife owns a 2003 Ford Escape. Sometimes when she applies the brake, the pedal will not depress, but the car continues forward in jerks, so I think some braking is happening.

This happens on a sporadic basis and is totally unpredictable. The dealer cannot reproduce the problem. It has happened 11 times, the first time at around 10,000 miles and then 10 more times over 60,000 miles. It seems to be getting more frequent.

There was a recall on the accelerator cable that described what is happening to a T, except for the resistant brake pedal. They have been over that several times and find nothing amiss with the cable.

Any ideas? My wife and I are at wits' end because we have jerked our way through at least two red lights (fortunately traffic was light).

A The "hard" brake pedal with the engine running is usually a sign of a problem with the power-brake vacuum booster. Ask your wife if the brake pedal when the problem occurs feels the same as it does after shutting off the engine and pumping the pedal a half-dozen times. With no vacuum available to help apply the brakes, the pedal will feel almost rock hard. A leak in the vacuum line, check valve, or brake booster could cause this, as could a low engine vacuum at the time the brakes are applied.

I agree that the throttle cable probably isn't the problem, but my Alldata database pulled up another recall, 07S51S1, dated June 2007, involving corrosion on the antilock brake system module connector. Ask the dealer to check this, and check for any problems with the vacuum brake booster system.

Q We have a '96 Olds Cutlass with the 3.1-liter V6 engine. It was running real good, just a little down on power. Then, two weeks after an oil change, the car would start to lay down on us and then the motor started knocking. The oil level is OK. Do you think it could be the exhaust being plugged, or is it internal?

A Internal engine noises, particularly knocking sounds, are never a good sign. If a connecting rod or main bearing is seizing, the tremendous friction will cause a loss of power. Use a mechanic's stethoscope to locate the source of the knock. If it's coming from inside the block itself, it's probably a serious engine problem.