Ray Magliozzi, syndicated columnist

Dear Car Talk: I have a 2003 GMC Sierra.

Sometimes it won’t crank or start. Nothing. All the usual stuff has been checked out — battery, starter, alternator, fuses — and I’m told they’re all good.

I did twist the exhaust pipe and bent it and starting it after that, I’ve had this problem intermittently. Could it be the bent exhaust pipe? — James

I don’t think so, James. I made a list of 1,000 things it could be, and a bent tailpipe came in around number 997, just above intervention from aliens visiting from Pluto.

If you creased the exhaust pipe and restricted the flow of exhaust completely, that could prevent the truck from running.

It would be like sticking a potato in the tailpipe. If the exhaust can’t get out, then fresh gasoline and air have no room to come in, and the car won’t run.

But even then, the truck would still crank. And you say that when this happens, it doesn’t even crank. You also say this problem happens on and off, and I doubt the exhaust pipe is bending and unbending itself while you’re inside watching “Young Sheldon.”

Let’s assume your mechanic checked all of the connections to the battery and alternator. Those can corrode over 20 years or come loose and cause the truck not to start some of the time.

If all the connections are solid, the next thing I’d try is a Neutral Safety Switch. That’s a switch that prevents your truck from starting unless the shifter is in Park or Neutral. When that switch fails, it can prevent the truck from cranking even when the shifter IS in Park or Neutral.

One simple (though not conclusive) test is this: When the truck fails to start, put it in Neutral instead of Park and try again. If it still doesn’t start, leave it in Neutral and turn the key to the crank position with your left hand while nudging the shifter toward Reverse and then Drive with your right hand.

If that gets it to start, that adds weight to the Neutral Safety Switch theory. And if that doesn’t fix it, you might try replacing the starter anyway. Starters do fail intermittently. A random failure to crank is a classic symptom of a failing starter. When your mechanic tested it, it may have worked fine. But that doesn’t mean it’s working fine 100% of the time.

If none of those suggestions pan out, James, write back, and I’ll give you numbers 4-10 on my list. Good luck.

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