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Very hot conditions can cause strange things to happen

11 months 27 days 23 hours ago |1054 Views | | | Email | Print

Dear Tom and Ray:


On a cross-country summer trip to Las Vegas, we stopped for gas in a town in New Mexico. After filling our ‘04 Ford Escape, it would crank but would not start. After a few attempts, I decided to stop so as not to kill the battery. Just down the road, there was a truck repair station. I gave them a call, and the owner towed my car into his shop. As he worked on it, it did start up. He hooked up a scan tool, but could find no codes to indicate that anything was amiss. As he was checking under the hood, he put a wrench on the battery clamps, and he said he found that the ground side was loose. He said that could have been what kept the car from starting. After paying the man, we drove to our destination and back to the East Coast with no problems. A friend of mine said that what the guy told me was impossible, and that a loose ground wire would not stop the car from starting. What is your opinion? — Charlie


RAY: A loose ground cable certainly can cause your car not to start, Charlie. But not in the way that your car didn’t start.


TOM: If the ground cable was so loose that it was no longer making contact with the battery post, the car would do nothing when you turned the key. You said your car cranked but then failed to start. So we know battery power was getting to the starter motor. That means the ground was connected.


RAY: So something else caused your car not to start. The truck mechanic did the right thing by checking for trouble codes in the computer. It’s often the case that if a problem occurs only once — or even just a few times — a code won’t be stored.


TOM: And unless there’s a code, once the car is restarted, you really lose your diagnostic opportunity.


RAY: So if it happens again, you’ll need someone to re-scan for codes. And if none are found, then he’ll need to work on the car when it’s actually in this “non-start” mode. He’ll need to do some tests to figure out what’s preventing the engine from getting either spark or fuel.


TOM: If I had to take a wild guess without the benefit of looking at the car, I’d suspect the crank angle sensor.


RAY: We’ve seen the crank angle sensor misbehave under very hot conditions. And that’s exactly what you were dealing with. You were driving across the country, so you presumably had been on the highway for hours — maybe all day. You were in the desert Southwest, and we know the desert can be, what? Hot! You stopped the car, and shut off its cooling functions, while you got gas. That’s what we call a “hot soak” condition, where the engine temperature spikes after the car is turned off.


TOM: I’m guessing that the heat caused an open circuit in the crank angle sensor, which sits in the hottest part of the engine, near the flywheel. The sensor then sent an erroneous signal to the car’s computer, and that’s what prevented it from starting.


RAY: After you had it towed, it cooled off enough to restart. And those exact circumstances weren’t duplicated during your trip.


TOM: It could be an open circuit somewhere else, but that’d be my first guess.


RAY: And if you’ve really had no problems since, and the circumstances were like those I described (which would be unusual for you during your day-to-day East Coast life), you could simply continue to drive the car and assume that it won’t be a problem again.


TOM: But if it’s causing you to live in fear, or you’re planning another long, steamy trip, then you can consider replacing the crank angle sensor for a couple of hundred bucks.


RAY: You’re going to ignore it? That’s what I thought. Good luck, Charlie.


A question with teeth

Dear Tom and Ray:


My husband and I disagree about whether the button on the parking brake should be pressed down prior to engaging and lifting it. If you don’t, it makes a grinding sound, and I think that can’t be a good thing. My husband contends that it makes no difference. Please settle this for us. Thanks. — Carolyn


RAY: I’m so glad people are finally writing to us with questions worthy of this illustrious column!


TOM: It makes no difference, Carolyn. The button is there to release the parking brake. That’s why it’s called the parking brake release button.


RAY: The clicking you’re hearing is a ratcheting mechanism that holds the parking brake in place once you apply it so it doesn’t release on its own and let your car roll away.


TOM: There’s a metal wheel at the base of the hand brake handle. That wheel, which is called a “ratchet,” has a bunch of teeth in it. Then there’s a metal spike called a “pawl,” which sticks into those teeth as they go by. The pawl allows the handle to go in one direction (up) but not the other (down). So all you’re hearing as you pull up the brake handle is that pawl clicking into each successive tooth.


RAY: When you push in the button, you’re pulling the pawl back, out of the way of the teeth. That’s why it doesn’t click. And that’s why pushing the button allows you to move the handle in both directions.


TOM: But it’s not necessary to hold in the button while you’re applying the brake. On the other hand, it does absolutely no harm. That ratcheting mechanism will last for the life of the car whether you let it click or not.


RAY: So, it’s an aesthetic decision, Carolyn, not a mechanical one. If you find the clicking sound pleasing, or reassuring — which I do — then just pull up on the parking brake handle and let it clack away.


TOM: But if it causes you distress and heartache, then feel free to eliminate that sound from your life by pushing in the button when you engage the parking brake. It doesn’t matter to the car.

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