Ray's Column: Mechanic says "I have no idea what's wrong!"?

In Ray’s column today (1.18.24), the cat was stolen from the reader’s car. The mechanic then replaced the cat, rear o2 sensor, plus did a few routine maintenance items. The reader immediately after this work noticed a significant reduction in engine power and very poor mileage. The reader takes the car back to the shop for an explanation. The mechanic said (apparently) they have no idea what is causing the symptoms. No idea? It seems like a pro-mechanic should easily be able to come up w/several potential causes for a major symptom like this occurring immediately after the work was done, and propose a testing plan to eliminate each, one by one, until the come up with the cause. Why do you think the mechanic couldn’t do that?

  • The reader is misrepresenting what actually happened?
  • The mechanic who did the work is good at wrench-turning, but doesn’t have the needed diagnostic skills?
  • This just isn’t the mechanic’s job ?

The second choice.

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But then wouldn’t the mechanic suggest the car needs to be scheduled in with the shop’s diagnostic expert, or taken to a different shop? Maybe the explanation is a little of number 2, and a little of number 1.

It’s definitely not #3 because if it’s not the mechanic’s job, then whose is it? Accountant? Engineer? Senator? :grin:

Not everyone is capable of performing diagnostic work. Some mechanics only change oil and repair exhaust systems.

my first guess? The mechanic is along the lines of “I know somebody who can do it cheaper…”

Unsure what you mean? Are you thinking the mechanic is trying to avoid a customer-relations situation about who is responsible to pay for the extra work needed to resolve the problem? After all it is possible the problem is not related to the prior work, just a coincidence.

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President. The buck stops with him. :wink:

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Sure, but in what other trade industry would we make that distinction when they took took the job and our money? If they took the job, the assumption is that any issues that arise as a result of the work should be addressed by who performed the work. Would we give a pass to a plumber or electrician in the same circumstances? Or, if an accountant prepared your tax return and, after the return was completed and paid for, you had a question about a specific deduction, to which they replied “I have no idea!”. In the eyes of the consumer, the shop’s inability to answer the question or attempt to diagnose it is all the more reason to suspect they did it improperly in the first place.

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I’d rather the mechanic said this then just start throwing parts at the problem.


In virtually any other trade or industry.

A windstorm blows shingles off my roof. I ask a roofer to repair it, which she does. After the repair I notice water leaking in around my front window. The roofer will need to call in someone else.

I chip a tooth eating some granola. The dentist does a root canal and crown but the tooth still hurts. I get referred to an oral surgeon for an implant.

My son breaks his finger playing baseball. The doctor applies a splint but the finger doesn’t heal straight, so the doctor sends him to an orthopedist.

A catalyst is stolen from a car. Car is towed to an exhaust shop to install a new one along with a missing O2 sensor. After replacing the missing parts the car does not run well. Engine performance diagnostics is beyond the scope of the exhaust shop, the customer is referred elsewhere.

If the technician installing exhaust should also be performing upper level diagnostics, does it follow that the diagnostic expert should be hanging mufflers?


Who says the works was done at an exhaust shop? There’s no reason to believe that’s the case.

Look, I understand where you’re coming from and I don’t totally disagree. I was a tech and did dealer tech assistance for many years and understand the vast difference in capabilities from Shop A to Shop B. My point isn’t that the shop that installed the cat & O2 sensor should know how to fix the driveability issue. I’m just saying that it’s not unreasonable for the customer to assume that the shop can fix the reduced power/mileage issue because, in their mind, it was caused by the cat and O2 replacement. Right or wrong, they will likely be surprised to get referred somewhere else at an additional cost.

But, if it was an exhaust shop then, sure, I agree with you.

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Sounded like it was their regular mechanic, Ray offered a few suggestions of what it could be but most required some trial and error by the shop. Confirming there isn’t an obstruction somewhere the exhaust system.