Prudent service personnel never overlook the "fingerprints" of a previous repair.
Evidence of someone else's work may be the most-valuable diagnostic clue to solving the customer's problems.
Through the years, I often get the feeling that I'm seeing the same movie over and over. Namely, I'm watching a technician struggle with a diagnosis simply because he or she is ignoring evidence of previous repairs. Many times, the location of the customer's complaint is right where human hands last touched that vehicle.
The best diagnosticians I've encountered usually are the best detectives. In turn, the best detectives usually are the most observant and inquisitive breed of people. They look at a "crime scene" and watch for things that don't look normal. Meanwhile, a detective-like technician keeps an eye peeled for signs of sloppy, ham-handed or incompetent repairs.
The next thing a competent detective-technician does is record the findings on the work order and alerts the service manager. Then the competent and mature service manager promptly alerts the customer. On the one hand, all service personnel hanker for simple, in-and-out repair jobs. But they also should be mature and professional enough to recognize a repair situation is not a slam-dunk—and react accordingly.
By the way, a capable service manager also understands that bad news, such as a bungled previous repair, doesn't get any better with time. The sooner it's explained to the customer, the better.
A detective encounters a wide range of clues from the more-obvious to the most-subtle—everything from a distinct, unusual footprint to the lightly scraped window frame. Likewise, good automotive diagnosticians may see a variety of clues. Hopefully the clues caution technicians that all may not be as it appears because someone else got under the hood before they did.
For example, a routine task such as checking fluid levels may steer a tech toward a major problem. I recall instances where I habitually checked the oil and discovered milky-looking oil, which suggests a condition such as excessive condensation and/or a coolant leak. A second look revealed a clean intake manifold and fresh gasket sealer oozing out of the intake gaskets.
OK, time to speak to the customer because someone has replaced the intake gaskets recently and coolant's leaking into the oil. Ultimately, this is an engine failure waiting to happen.
Another time, I was checking a Toyota for an evaporative emission trouble code. During a visual check of the engine compartment, I realized something didn't look normal. Then I realized that the original-equipment hose clamps were missing from two of the "evap" system hoses. Closer inspection revealed that someone had reversed the two hoses on an evap valve. Reinstalling the hoses correctly fixed the car.
These are just two convenient but useful examples. In both instances, the vehicle owner wasn't thrilled to hear what I found. But the fact remains that intake gaskets don't change themselves—not to mention leak. No, human hands did that. Likewise, emission hoses don't miraculously swap positions on a purge valve.
On the one hand, you don't want to cause trouble, but cautious service personnel should document these kinds of findings on the work order and explain them to the vehicle owner. I know of more and more shops that are documenting findings with inexpensive digital cameras.
Politely but clearly cover your tail by explaining your findings. This eliminates or minimizes the risk of your service personnel becoming entangled in potentially costly mistakes.
More often than not, vehicle owners will appreciate your candor and professionalism. And this will earn their trust and loyalty. Things like trust and loyalty must be earned—you just earned them, didn't you?