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What you will learn:
•Even identically build vehicles should be treated individually•Always ask 'why' to get to the root cause of a failure
•To increase efficiency and accuracy in diagnosis and repair
An automobile is a compilation of many systems that work together to make a single, get-up-and-go and stop-when-you-need-to vehicle. It's almost biological. In the same way that the nervous system depends on the cardiovascular system, and the cardiovascular system is useless without the respiratory system, the drivetrain depends on the engine, and the engine is useless without the fuel delivery system. When a system includes several different components, each component is reliant on the others. Every vehicle is different, even when they're the same make and model year; they need to be treated accordingly. A 2010 F150 with 150,000 miles, used on construction sites is a different truck than a 2010 F150 with 60,000 miles that carries home groceries every Sunday.
Seeing the big picture
"Big Picture Diagnosis" is the practice of scrutinizing the vehicle, taking in what it is. It's not just the year, make, and model, but condition, use, and abuse. Finding a defective component or seeing a newly installed part should raise the question, "Why did this go bad?" A new bumper bracket could mean a crash. One new tire or wheel might mean a curb hit or an encounter with a pothole. High-flow exhaust or an aftermarket air intake system is a good sign that a performance tune may have been installed in the engine control module. Every vehicle has a history to reveal, from the rubber remnants of past burnouts on the quarter panel to uneven front tire wear on a pickup, suggesting payload overload. Factors like rust, usage, and maintenance schedule determine the plan of attack when diagnosing and servicing a vehicle. Familiarizing yourself with the entire vehicle aids with the diagnosis and helps find the factors that could prevent your repair from coming back.
Finding the failed part is rarely the end of the diagnosis. That broken rear stabilizer link may be the cause of the customer's complaint, but if you don't replace those leaking, rebounding rear shocks, your repair might have a short shelf life. Sometimes, the component causing all the racket isn't defective at all; it's only reacting to an actual failure. A noisy variable cam timing actuator could result from a lack of oil supply to the solenoid. The lack of oil supply could be due to a blockage, and the blockage might be pieces of filter media detached from a cheap oil filter. The root cause of failure: Oil filter. I watched this scenario play out; it wasn't pretty.
Besides looking deeply into the diagnosis to verify the cause of the failure, we also need to notice those things that could mimic the symptom we repaired or create an "ever since you worked on my car" situation. This article consists of automotive service scenarios that happened. Every story is true and demonstrates the importance of looking past the obvious and seeing the big picture.
Lincoln coolant leak
A Lincoln come into our shop with an overheating concern and small green antifreeze drops on the customer's driveway. The coolant was almost empty, and the technician found a leaking heater hose at the rear of the engine. He completed the repair, checked for engine damage (from the overheating), and shipped the job. The next day the customer returned, claiming that she still saw green drops in her driveway. My first thought was residual antifreeze left over from the repair. I gave the keys to the tech and asked him to check it out. The refrigerant leak detection dye is green. Enough said. This repeat repair was only a repeat repair because the technician serviced a system (in this case, the cooling system), rather than the entire vehicle (Figure 1).
It's not the brakes, but it's broke
Here's another example of constricted vision causing unrestricted customer dissatisfaction. A vehicle pulled into our service drive with an unmistakable, strong, burning brake smell. The repair order said, "Customer states that he smells something burning." The technician replaced the sticking right front caliper, right front rotor, and front brake pads. Two days later, the customer returned, claiming that he still smelled something burning. I drove the vehicle, and there was an obvious oil-burning smell at idle.
Further investigation revealed that the all-wheel-drive power takeoff unit was dumping oil all over the exhaust pipe behind the catalytic converter (Figure 2). Ask this question: "What else could cause a symptom similar to the concern I'm repairing?" In this case, the two components are in entirely different systems and have very little in common. Yet to the customer, a burning smell is a burning smell.
New parts on a vehicle always have a story to tell, especially if the previous repair is related to the concern you're diagnosing. New coils and spark plugs most likely mean that someone was trying to fix a misfire. EGR valves and MAF sensors seem to be popular parts fired from the diag-cannon, when the do-it-yourselfer takes a shot at the repair. The average person doesn't understand the importance of using good quality parts, and there are a lot of bad parts out there. Don't assume that because a part is new, it's functioning correctly. You can save yourself a lot of time by scrutinizing the last person's repair.
Exploring the Ford Explorer's lack of heat
A 4.0L Ford Explorer came into our shop with no heat. The engine wasn't reaching operating temperature, and the coolant level was full with no leaks. The technician suggested replacing the thermostat. While looking around under the hood, we saw new hardware attaching the upper thermostat housing to the lower thermostat housing (Figure 3). So, now it's reasonable to assume that someone either replaced the thermostat or left it out entirely. Since we knew that the cooling system had been opened, there was also a very good possibility that the lack of heat was due to air intrusion. We decided to vacuum-bleed the cooling system before proceeding with further diagnosis. The coolant level dropped about a pint after bleeding the system. The engine reached operating temperature, and the heat worked fine. The new hardware on the thermostat housing was our clue to suspect an air pocket, saving an unnecessary thermostat replacement. Sometimes, it's not the things you find that are causing problems today, but it's the “okay today, bite you in the wallet tomorrow” things that make it worth the time to look just a little bit harder.
Fixing a 'comeback' before it ever left
Our technician diagnosed a canister vent valve as the cause of a P0455 (“EVAP large leak”), which illuminated the check engine light. It was a good diagnosis. After replacing the part, the EVAP system passed the performance test with flying colors. While giving the engine compartment one more quick look-over and before installing the engine cover, he found that the MAP sensor hold-down bolt was backed out of the intake manifold about halfway (Figure 4). The sensor was still sitting flush on the manifold, but probably not for long, especially since it was a turbocharged engine. It would have taken only a tiny amount of air to bypass the MAP sensor, for the check engine light to pop on with a "system lean" DTC. The customer doesn't know EVAP from MAP and doesn't care. The check engine light coming back on is all that matters.
A misfire's missed opportunity
Another example of "finding it now or finding it later" is a 4-cylinder Ford Escape that received a new torque converter (due to an intermittent shudder when accelerating at highway speeds). When engine load and throttle position were just right, the torque converter clutch would slip, causing a vibration. After the technician performed the repair, I road-tested the vehicle, and the shudder was gone. After a post-repair road test, I always open the hood and poke around. I found a puddle of new engine oil in the valve cover valley alongside the ignition coils (Figure 5). The oil came straight from the filler and was spilled during a recent oil change. It was impossible to tell how much oil had gotten into #3 and #4 spark plug wells without removing the coils. We've all seen how a spark plug well full of motor oil can turn coil boots to mush, causing a misfire. We also know how similar a misfire can feel to a torque converter shudder when accelerating on the highway. It's all about customer perception. When seeing the big picture, it's important to question what you see. Clues are everywhere if you see them for what they are.
Short circuits can lead to long days
I was handed a 2017 Ford Explorer that was blowing the interior lamp fuse. Cargo lamps, courtesy lamps, glove box lamps, puddle lamps, vanity mirrors, and other illuminated components were on that same fused circuit. After checking the obvious and easily accessible, I noticed in the wiring schematic that part of the harness ran under the right-side rocker panel interior trim. The area under a rocker panel trim is commonplace for a wire rub-through to ground. The area tends to ingest water from doors open during a rainstorm, and the constant foot traffic isn't very healthy for a wire harness. So, if the harness goes that way, I always check it. What I found under the rocker trim was broken glass, the kind of glass you'd expect to find if the passenger window had been broken (Figure 6).
A busted-out door window could mean water inside the door. The harness for the right-side puddle lamp (which is on the shorted circuit), runs through the door, so I removed the right front door panel. The circuit splice was corroded and leaning against the window track, creating a short to the ground. If I had ignored the glass, I could have spent an entire day, or more, trying to find the short to ground. Don't ignore the clues. Just another example of why it's essential to ask, "Why did this go bad?"
An unclosed door reveals an open opportunity
A Lincoln SUV came into the shop with a rattle in the rear over bumps. It didn't take much of a road test to realize that the rattle was coming from the liftgate. Further inspection revealed that the liftgate wasn't properly closing. The gaps on the sides of the liftgate showed that the liftgate was out of adjustment. The liftgate opened and closed smoothly and the hinges were tight. The workshop manual showed that the liftgate hinges are adjustable. But why would a liftgate lose its adjustment, especially when the hinges are in good condition?
We put the vehicle up on the lift and found that the right rear corner of the body (behind the bumper) was crunched (Figure 7). There was a hole in the body at a seam. The damage twisted that section of the unibody just enough to tweak the liftgate position without causing any visible damage on the outside of the vehicle. We sent it to the body shop.
A silent killer
Here's something else to look for. When diagnosing or repairing an electrical concern, check the battery for leakage and battery terminals for corrosion. Battery acid is a silent killer. A slowly leaking battery will destroy any wires that dare be in its path (Figure 8). The wire repair you performed today on the right rear of the vehicle could go bad tomorrow due to battery acid leaking in the left front of the engine compartment. If you see a dirty, leaking, corroded battery (or terminal), make that repair a part of your entire electrical repair. Clean the area under the battery before rogue electrolyte fouls up your repair.
These real-life scenarios are likely nothing you haven't already seen. I teach all the young techs who are just starting in the business, the concept of "Big Picture Diagnosis." The mantra of the automotive technician should be "check, check, and triple-check."
Every diagnosis of a faulty component or a shorted circuit should be immediately followed up with the question, "Why did this go bad?" Every part in every system links up with every other part in every other system, somewhere down the line. When an obstructed catalytic converter causes a hard brake pedal (due to a loss of engine vacuum), or when a leaking heater hose causes an engine to misfire (because it's leaking onto an ignition coil), a system is affected by the interference of a seemingly unrelated system. Look past the obvious and learn from it all.
E-mail me your big-picture diagnosis stories. Maybe your experience can save me a headache somewhere down the road. Learning from our own mistakes is good; learning from someone else's mistakes is even better. Keep your eyes open, and always ask, "Why did this go bad?"
