There’s one situation every professional automotive technician has had to deal with from time to time, and it involves the home-grown garage guy who just so happens to own a couple of ratchets, a repair manual and a broken-down car.

Some of these connoisseurs of the all-knowing repair manual skim through sections without truly comprehending them. Many just assume they already know how a certain system works based on previously having some luck on another system. And, after they’ve turned a few screws, glanced at a few more pages, and found their problem isn’t solved, then, and only then, do they head to a real repair shop. Of course, their repair manual is always laying on the passenger seat with the important pages carefully marked for the shop tech to examine.

In a recent case, the car in question wouldn’t start, and a neighborhood mechanic did his best to read and understand what was on the diagnostic pages of the manual, but he couldn’t make any sense of the wiring diagram for the fuel pump circuit. His final verdict, “It’s not getting any voltage to the fuel pump.”

This was one of those cars where the fuel pump doesn’t turn on until after the first spin of the crankshaft. In a lot of systems, especially older ones, turning the key on would at least let the fuel pump relay run for a few seconds, but not on this car.

I checked the signal according to the manufacturer specifications and, sure enough, the voltage (and ground signal) was at the fuel pump. All it needed was a new pump.

Now, the other half of dealing with the weekend mechanic is explaining the diagnostic results at the service counter. As usual, there’s a bit of distrust and an attitude accompanied with his response.

So, while still trying to be a professional in my latest run-in, and at this point somewhat of a teacher too, I answered his remarks with my own sarcastic response, “This vehicle doesn’t turn on the fuel pump relay until it knows you’re going to start it. Meaning, until the engine spins and sends a cam/crank impulse to the PCM, the fuel pump relay isn’t energized.

“The fuel pump fuse is activated after the relay, and since the relay isn’t on, there won’t be any voltage at the fuel pump fuse. But, I’m sure you knew all of that, because you had the page marked for me in your repair manual. In fact, you had it highlighted, too.” The expression on his face was priceless.

I know he’ll be back in about a year or so. How do I know? Because he did the very same thing with the very same car last year, and it had the very same problem. Of course, just like last time, he’ll run down to the same cheap-o parts store and buy the same bargain-basement fuel pump that might last another year or so, if he’s lucky.