Auto Service World
Feature   April 1, 2000   by Rick Cogbill

Sensors and Sensibility

Good technicians make their own diagnosis.


Beanie hung up the phone. “Mrs. Tidbit is having her 1988 Plymouth Horizon towed in; she wants a new fuel pump. Should I order one up?”

“Nope,” I answered. “And who says she needs a fuel pump?”

“Her husband,” said Beanie. “He can make it run momentarily by pouring fuel down the throttle body. Sounds like fuel pump to me.”

He tried to look like a dedicated employee, doing his utmost to satisfy a customer. But I could see he was just itching to visit with the parts delivery girl again. Enough of this making time on company time, I thought.

“Good technicians make their own diagnosis,” I said out loud. “Ordering unnecessary parts wastes time and money.”

Soon the little car was in the bay, with the hood open. All of us stared at the engine, lost in our own thoughts.

“Most peculiar,” mused Basil.

“Very interesting,” I agreed.

“Beats me,” resigned Tooner.

“Weird,” said the Bean.

“Crank the engine again,” I said to Basil.

He obliged, and even without adding extra fuel, the Horizon would fire up, and then quit.

Fuel pump pressure was good, and the ignition system produced spark right to the bitter end.

“Look at the data stream,” said Tooner, pointing to the scanner. “The TPS, MAP, and Coolant sensors all read funny. Looks like a bum computer. I’ll order one up.”

“Nope,” I said, for the second time that day. “Betcha each a donut I know what’s wrong.” I unplugged all three sensors. “Try it now,” I called to Basil.

At coffee break, as I started on my third chocolate donut, I explained my secret of success. The car had started with the sensors unplugged, although it ran rough. Then I plugged the sensors back in until one of them caused the engine to stall. In this case it was the MAP sensor; it was internally shorted.

“Yeah,” said Beanie in amazement. “But where’d you learn that trick?”

“Ah, enlightened one,” interjected Basil, “you discern correctly, for indeed it was a trick!” He eyed my donuts longingly. “First played on us by an instructor at a training course we took — am I right?”

“Yep,” I said between bites. “He shorted a sensor on our test car with a paper clip, then made us find the problem.”

Basil continued, “Those sensors all run on the same 5v signal from the ECM, and if one shorts to ground, they all short out.” He licked his lips. “Are you sure you can eat all those by yourself?”

“And,” I finished, ignoring him, “we also learned that if you unplug a sensor and the car runs better, the sensor is probably sick. Since I didn’t know which one, I unplugged them all.”

Tooner pushed the donut box towards me. “Here, Boss. Have another.”

I looked at the sticky buns, and began to feel sick myself.

“Nope,” I mumbled, for the third time that day. “I think I’ve had enough.” SSGM

About The Writer

Rick Cogbill has been writing for about two years, including a weekly auto advice column in four British Columbia newspapers. He also writes a bi-weekly humor column for another paper, and does freelance work for Okanagan Life, Okanagan Business, BC Christian News, The Evangelical Baptist, and Western People magazine. Cogbill earns his living as an automotive service professional. He owns and operates Rick’s Automotive Services Ltd., located in Summerland, BC, about 250 miles east of Vancouver in the Okanagan Valley, near Penticton. It is a five-bay shop, which he built about eight years ago. He has run his own business for 10 years, and earned a living as an automotive technician for more than 24 years. Tales of Basil, Tooner and the Bean come from actual cases that happened in Cogbill’s shop, though he has changed some of the details to add humor, and to avoid the possibility of being sued by irate customers. Each story contains a genuine nugget of technical service wisdom, which is based on actual vehicle work orders, not just theory.


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