Dear Car Talk:

I have an '06 Pontiac Vibe. It's a stick shift that I lovingly refer to as "The Ponticorn," since stick shifts these days are so rare. If I park in my driveway, which has a steep-ish downhill grade, my car starts without a problem every time. If I park in front of my house on the street, which is flatter, the engine won't budge one out of three tries. It behaves as though I am not pushing in the clutch (which you have to do in order to start the car). So I release the clutch and push it in again. Most times, it will then start. Sometimes it takes a third attempt. Why in the world would this be happening?

-- The Pontiprincess

Sounds like you've got some Ponti-paranormal activity going on there, Princess.

My guess would be that you're on the right track in focusing on the clutch pedal. There's a switch called an "interlock" that prevents the car from starting unless you have the clutch pedal pressed all the way in.

It's a safety feature. If the car is in first gear, for instance, they don't want you to turn the key and lurch the car through your garage door. Or worse, over someone standing between the car and the garage door.

The clutch interlock switch itself is not affected by gravity or angle. But you are. And if it's just starting to fail and not making a good connection, it could be that when the car is angled down the driveway, gravity is working with your body weight to put a little more force on the clutch pedal when you step on it, and that's enough -- right now -- to engage the switch. But when you're on flat ground, on the street, without that extra force, the switch works sometimes and doesn't work other times.

Before you do anything else, check to make sure nothing is in the way of the clutch pedal. We've had customers come in with similar complaints, and sometimes we were able to solve the problem by simply removing a floor mat that had gotten bunched up under the pedals. We only charge $300 for that service.

But if there's nothing preventing the pedal from reaching the floor, you can ask your mechanic to "jump" the clutch interlock temporarily, as a test. That means, basically, leave it out of the circuit.

Obviously, you need to be careful while the switch is not functioning. But if you remove the interlock switch from the equation and then the car always starts perfectly on level ground, you've diagnosed the problem. Then you can have your mechanic put in a new switch.

If that doesn't fix the problem, these cars are also known for starter-motor solenoids that fail. So if it's not the clutch interlock, you probably need a starter motor, Your Highness. Good luck.