Wayne Catlett is a mechanic with the Department of Vehicle Services for the County of Fairfax, Virginia, where he has been employed since 1985. Catlett mostly works with engine performance and wiring issues on a daily basis.
In his bay he has a dyno chassis, where he checks on everything from engine performance to speedometer calibrations. Some of Catlett's time is also spent on multiplexing to identify specific problems.
"Things are changing constantly," Catlett says. When I first started it was all gasoline engines and it was pretty simple. Now everything is basically in 'computer talk'," he continues, and compares the use of technology such as e-mail to the technology he uses everyday in his job.
"I struggle with e-mail, yet I spend the majority of my day on a laptop computer diagnosing vehicles," he says.
When a laptop recently crashed at his shop, he realized how much he depended on technology in his everyday work.
"I was like a fish out of water," Catlett says. "There are hand-held scanners in smaller garages that do the same thing and give the same information as a laptop. But with a laptop you can view a lot more things at once.
Some of Catlett's biggest challenges come from the vehicle's electronics. He says that once a technician understands how circuits operate, similar techniques can be applied to a completely different vehicle. "The majority of vehicles now are working more off of a ground circuit, or using the ground to open and close circuits," Catlett says. "If you use the ground wire to open and close the circuit it's easier on them."
He adds that he first tries to identify a common problem in a circuit that could be leading to the vehicle's demise, such as a sensor or a broken wire, but recommends finding the problem in sequential order.
"With electronic engines, even though you might have a certain sensor acting up or giving you a reading, it's tied into several other procedures or several other sensors," Catlett says.
Patience is definitely a virtue in diagnosing electronic problems. "I don't want to jump the gun and feel like I'm wasting my time. You can't complete step three until you complete step two," Catlett says. "It's hard not to at times because you're so pressured."
Catlett explains that the majority of vehicles now are working more off of a ground circuit, using the ground to open and close circuits.
"Once you know how circuits work, you start understanding how the circuits operate then you can apply it, even to a completely different vehicle," he says. "Despite what a lot of instructors have told me, we work with a lot lower voltages and amperages and the old 'test light' method is not recommended for any type of computer-checking because it can cause serious issues.
Ideally, the DVOM or multimeter tester is used for this, and if all the schematics are available and the technician knows how the circuit operates what and the common components are, the wiring can be used to disconnect or short things out intentionally to try and re-create certain conditions, Catlett says.
SOLVING A MYSTERY
Catlett recalls a situation in the shop when a vehicle wouldn't start, and he pinpointed the problem to the injector, exhaust back pressure, engine oil pressure and manifold air pressure sensors. He tried to start the vehicle, to no avail. "The tach didn't work, and I was outside and didn't have the laptop with me." Even after Catlett put a cam sensor in it, nothing changed.
That's when he started using his multimeter tester and found that all four circuit units shared the same voltage reference. The exhaust backpressure sensor of approximately 5.3 volts shorted out, and took the voltage away from everything else, Catlett continues.
"An exhaust backpressure sensor is normally not something that will affect the no-start condition," he continues, "but because it shared the same voltage reference as the cam sensor, all the voltage was drained, so there wasn't any voltage left for the cam sensor, and in turn created the no-start."
When Catlett compared the incident with readings on the laptop to the wire schematics, he found the voltage references were indeed the common problem between all of the sensors.