The Danger of Tunnel Vision in Automotive Diagnostics: Anchoring, Confirmation Bias, and Premature Closure [E243]
About this episode
When a Dodge Durango is brought in for a second opinion on a supposedly slipping transmission, a simple test drive reveals a surprising truth: the vehicle is just stuck in four-wheel-drive low. Host Matt Fonsland uses this real-world diagnostic blunder to explore the psychological traps that technicians fall into, including anchoring, confirmation bias, and premature closure. Discover how a flashing green light and a quick look at the owner's manual saved a customer from an unnecessary transmission replacement, and learn valuable lessons on avoiding diagnostic tunnel vision in the shop.
Thanks to our Partners, Pico Technology, and Autel
A Dodge Durango came into the shop for a second opinion after being suspected of needing a transmission. The symptoms sounded convincing at first: harsh shifts, apparent slipping, no diagnostic trouble codes, and a vehicle that felt completely wrong on the road. But the actual problem was much simpler. The Durango was stuck in four-low. Once shifted properly through neutral, the harsh shifting, driveline bind, and “slipping” behavior disappeared.
Matt uses the case as a springboard into a broader discussion about diagnostic tunnel vision. The point is not just that someone almost condemned a transmission unnecessarily. The deeper issue is how easily a first impression can become the diagnosis. Once the vehicle felt like it was slipping, everything after that could be interpreted through that lens. That is where anchoring, confirmation bias, and premature closure start to become dangerous.
The episode also compares the Durango case to a more common misfire scenario. A vehicle comes in with a misfire, the scan tool identifies a cylinder, the car line is known for coil failures, and the diagnosis becomes a coil and plug before much testing happens. That gamble may work most of the time, but the process failure is still there. Being right by probability is not the same as proving the fault.
Matt also shares a personal example involving a Mini Cooper that was nearly misdiagnosed as needing a turbo. The actual issue was cam/crank timing related. The mistake became a difficult but important lesson in responsibility, process, and making things right with the customer.
The episode closes with a nod to Mel Brooks on his 100th birthday, including Matt’s Mount Rushmore of Mel Brooks films: Blazing Saddles, Spaceballs, The Producers, and History of the World, Part One.
Key Topics
- Why the Durango seemed like it had a major transmission failure
- How four-low can mimic slipping, harsh shifting, and driveline problems
- The importance of reading the owner’s manual when unfamiliar indicators appear
- Anchoring, confirmation bias, and premature closure in diagnostics
- Why “incompetent” may be technically accurate but often incomplete as an explanation
- The ethical problem of charging for the wrong repair when the real fix is simple
- Why common failures can make weak testing feel justified
- How probabilistic diagnosis can work until it does not
- The value of owning a mistake and making it right
- Mel Brooks, comedy, and Matt’s Mount Rushmore of Mel Brooks films
Pull Quote Options
- “The first impression is often the most dangerous piece of data in the whole diagnostic process.”
- “Being right most of the time does not mean the process was right.”
- “Customers should not be paying for our anchoring, our confirmation bias, and our premature closure.”
- “The real danger is not being wrong. The real danger is being done too early.”
Episode Takeaways
- A symptom that feels obvious can still be misleading. The Durango felt like it was slipping, but the transmission was not the problem.
- A flashing indicator or odd message on the dash may be the clue. The owner’s manual may not feel like a diagnostic tool, but sometimes it is.
- Common failures can create lazy confidence. A known coil failure pattern or common turbo issue may point in the right direction, but it does not replace verification.
- Premature closure is expensive. It can cost the customer, the shop, or both.
- Ethics matter most when the mistake is discovered after the repair. The customer should not pay for a part that did not fix the vehicle just because the shop eventually stumbled into the real fix.
- A good diagnostic process should include forced questions: What am I anchored to? What evidence am I accepting too easily? What would prove my theory wrong?
Thanks to our Partner, Pico Technology
Are you chasing elusive automotive problems? Pico Technology empowers you to see what's really happening. Their PicoScope oscilloscopes transform your diagnostic capabilities. Visit PicoAuto.com
Thanks to our Partner, Autel
From drivability diagnostics and TPMS service to ADAS and advanced safety systems, Autel helps technicians follow OEM procedures and repair with confidence. Learn more at Autel.com
Contact Information
The Automotive Repair Podcast Network: https://automotiverepairpodcastnetwork.com/
Remarkable Results Radio Podcast with Carm Capriotto: Advancing the Aftermarket by Facilitating Wisdom Through Story Telling and Open Discussion. https://remarkableresults.biz/
Business by the Numbers with Hunt Demarest: Understand the Numbers of Your Business with CPA Hunt Demarest. https://huntdemarest.captivate.fm/
The Auto Repair Marketing Podcast with Kim and Brian Walker: Marketing Experts Brian & Kim Walker Work with Shop Owners to Take it to the Next Level. https://autorepairmarketing.captivate.fm/
The Weekly Blitz with Chris Cotton: Weekly Inspiration with Business Coach Chris Cotton from AutoFix - Auto Shop Coaching. https://chriscotton.captivate.fm/
Speak Up! Effective Communication with Craig O'Neill: Develop Interpersonal and Professional Communication Skills when Speaking to Audiences of Any Size. https://craigoneill.captivate.fm/
Matt Fonslow
"I'm Matt Fonsland. Humor is just another defense against the universe. That and more after a word from our sponsors..."
The host of this podcast, who is a professional mechanic and teacher in the automotive industry.
Matt Fonslow is an ASE Master Certified technician, shop manager, and automotive instructor who hosts the 'Diagnosing the Aftermarket A to Z' podcast. He is highly regarded in the automotive repair community for his focus on diagnostic methodology and technician training.
Pico Technology
"That and more after a word from our sponsors, Autel and Pico Technology. Are you chasing elusive automotive problems?"
A company that makes advanced diagnostic equipment for mechanics. Their main tool, an oscilloscope, acts like a heart monitor for a car's electrical system, showing electrical signals as visual waves.
Pico Technology is an industry-leading manufacturer of PC-based oscilloscopes and automotive diagnostic equipment. Their tools allow technicians to capture and analyze high-speed electrical signals from vehicle sensors and actuators in real-time.
ADAS
"From drivability diagnostics and TPMS service to ADOS and advanced safety systems, Autel helps technicians follow OEM procedures..."
The safety features in modern cars, like automatic emergency braking, lane-keeping assistance, and blind-spot monitoring. These systems use cameras and sensors that must be perfectly aligned to work safely.
Advanced Driver Assistance Systems (ADAS) are electronic safety systems designed to assist drivers with steering, braking, and parking. These systems rely on inputs from cameras, radar, and ultrasonic sensors, which require precise calibration after structural repairs or wheel alignments.
Dodge Durango
"And it was about a Dodge Drango that was brought, dropped off at the shop for a second opinion and really wondering, you know, if it indeed needed this part..."
A large family SUV made by Dodge. In this episode, a Durango was acting like its transmission was broken, but it was actually just stuck in a slow-speed off-road gear because the driver didn't put it in neutral to let it shift back to normal.
The Dodge Durango is a mid-to-full-size SUV that transitioned from a traditional body-on-frame truck platform to a unibody architecture in its third generation. Modern models feature sophisticated electronic four-wheel-drive transfer cases that require specific shift sequences, such as shifting into neutral, to transition between low and high ranges.
TCM
"Could I program the new quote unquote new transmission or TCM with the latest and greatest if it indeed needs the transmission?"
The computer brain that controls an automatic transmission. It decides exactly when the car should change gears based on how fast you are driving.
The Transmission Control Module (TCM) is an electronic computer that regulates an automatic transmission's operation. It processes sensor inputs like engine speed, wheel speed, and throttle position to command gear shifts and torque converter clutch engagement.
DTCs
"The complaint was very harsh upshifts. And the engine like slipping major slipping, that was the complaints. And there's no DTCs."
The technical codes stored in your car's computer when a warning light, like the Check Engine light, comes on. Mechanics read these codes to start figuring out what is wrong.
Diagnostic Trouble Codes (DTCs) are standardized codes generated by a vehicle's On-Board Diagnostics (OBD) system when it detects a fault. These codes help technicians pinpoint the specific system or component experiencing a malfunction.
four low
"And when I go around corners, it's hopping really bad. And then it dawns on me. This thing's in four low."
A special low-speed gear setting for off-roading or pulling heavy loads. It makes the car go very slow but gives it massive pulling power. If you try to drive normally on the street in this mode, the engine will rev very high and the car will feel broken.
Four-Wheel Drive Low (4-Low) is a gear range in a four-wheel-drive vehicle's transfer case that provides a high gear reduction ratio. This maximizes torque at very low speeds for extreme off-road conditions, but driving in this mode on dry pavement causes high RPMs, low vehicle speed, and driveline binding.
driveline bind
"Of course, there's no TTCs, it shifts normally, there's no more major wheel hop going around corners or driveline bind, if you will."
A jerking or hopping feeling that happens when you turn a four-wheel-drive vehicle sharply on dry pavement. It happens because the front and back wheels are locked together and trying to spin at the exact same speed, even though they need to turn at different speeds.
Driveline bind occurs in four-wheel-drive vehicles when the front and rear axles are locked together on high-traction surfaces like dry pavement. Because the outer wheels must travel further than the inner wheels during a turn, the tires must slip or hop to release the mechanical tension built up in the drivetrain.
anchoring
"Confirmation bias, anchoring and premature closure. I mean, that's about sums it up. So in my mind, and I could be wrong, the anchoring part was the first clue."
A mental trap where you focus entirely on the very first clue you get and refuse to change your mind, even when new clues show you might be wrong.
Anchoring is a cognitive bias where a technician relies too heavily on the first piece of information they receive (such as a customer's description of a 'slipping transmission') when making diagnostic decisions. This bias can cause them to ignore subsequent data that contradicts their initial theory.
confirmation bias
"Confirmation bias would be any and all information gathered, be it feeling, be it hearing their butt sensor, their sense of smell..."
A mental habit where you only look for clues that prove your original guess was right, while ignoring obvious signs that prove your guess was wrong.
Confirmation bias is the tendency to search for, interpret, and recall information in a way that confirms one's preexisting beliefs. In automotive diagnostics, a technician suffering from this bias will only focus on scan data or physical symptoms that support their initial theory, while dismissing evidence that disproves it.
premature closure
"And lastly, you have premature closure, little to no follow through. I probably have a better example of premature closure that'll rattle off..."
Stopping your investigation too early because you think you found the answer, without doing the final checks to make absolutely sure you are right.
Premature closure is a diagnostic error where a technician stops investigating once they find a plausible explanation or a single faulty component, failing to perform final verification tests. This often leads to misdiagnoses, missed secondary faults, or replacing parts that were not actually the root cause.
coil-on-plug
"Pick your car line, coil on plug. What's it need? Coil and plug. How many cars does that happen?"
A modern ignition system where every spark plug has its own tiny electrical coil sitting right on top of it to generate the spark. When these coils fail, the engine will misfire and run rough.
Coil-on-Plug (COP) is an ignition system design where an individual ignition coil sits directly on top of each spark plug. This setup eliminates spark plug wires, reducing energy loss and allowing the engine computer to control ignition timing for each cylinder with extreme precision.
Mini Cooper
"It actually reminds me of this mini Cooper. I think I talked about this one time when it first came in, the complaint was low boost or lack of power."
A small, stylish British hatchback owned by BMW. The host talks about a diagnostic mistake on one where a timing chain problem was misdiagnosed as a bad turbocharger.
The Mini Cooper is a sporty compact hatchback celebrated for its go-kart-like handling and turbocharged engines. Second-generation models (R56) are notorious for timing chain wear and tensioner failures, which can throw off engine timing and trigger cam-crank correlation fault codes.
cam crank correlation
"And I think it had one cam crank correlation DTC blow the codes out of it go drive it would set low boost codes all over..."
The perfect timing alignment between the top half of the engine (valves) and the bottom half (pistons). If they get even slightly out of sync, the engine will run poorly, and in some cars, the pistons can crash into the valves and destroy the engine.
Cam-crank correlation refers to the precise timing synchronization between the camshaft (which controls the engine's valves) and the crankshaft (which controls the pistons). If the timing belt or chain stretches, wears, or jumps a tooth, the engine control unit detects that these two shafts are out of sync and sets a correlation fault code.
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