who does the free diagnostic? nissan problem (missing)

Now you got that right. It does sell a lot of parts. O2 sensor lean indication code? Customer buys an O2 sensor after the "diagnostic." Two days later the code comes back because the original O2 sensor was truthfully reporting the REAL problem -- leaking intake manifold gasket. "EGR insufficient flow" code and they sell the customer an EGR valve. Two days later the code --caused by carbon clogged EGR passages -- comes right back. At least the "diagnostic" is free -- worth every penny it costs!

Don

If you're selling parts a "free" diagnostic is great investment. It's amazing the amount of money some people will spend to avoid having to pay for a real diagnosis.

Ive used them twice, since I have not invested in a code scanner yet. The first time it gave me a multiple misfire diagnosis, which confirmed my fears...that the Buick plenum had decomposed and was irrigating my cylinders. The second time it was quickly recognized to be due to a gas cap improperly seated (which the Autozone counterman recognized), and we just reseated it.

So for me, it has been helpful...

Even if a person has his own scanner, it will only point to the codes, it wont diagnose the problem. Throwing parts at cars is a very unreliable way to fix them.

Not true at all! The scanners at my shop have freeze-frame ability, data stream readout, KAM reset, factory tests, ability to write to the PCM. There is a HUGE difference between the code reader at AutoZone and a real scanner.

A scanner that is more than a code reader is frequently essential for diagnosis.

Don

Correct.

Again, I think we disagree more in semantics than philosophy. You have commercial quality diagnosis equipment.

There is a great difference between this, and what some people buy as code readers or 'scanners'. The AutoZone unit is okay for its type, but does not do the diagnostic work for you.

That's one hell of a counterman. ;-)

I wonder how he knew it was the gas cap and not a leaking vent solenoid?

He had seen it enough times that he 'suspected' it was the gas cap, but said it might be further in the system. We reseated and reset, and it turned out to be the answer.

Was a service to me because I had no code reader at all. And it worked.. I dont mind taking the car to a competent dealership or independent mechanic if needed, but would prefer to sidestep simple issues like the abovementioned.

IOWs, he was guessing.

AKA a lucky guess.

And had he guessed wrong, he'd already erased important freeze frame information making subsequent diagnosis that much more difficult.

The confusion occurs because many do not know the difference between a code reader and a real scan tool.

A code "reader" is not a "scanner."

Neither tool does the diagnostic work. A trained brain is still a very essential part of that step.

Although if he was wrong and the purge valve or another leak is causing the problem, the light will come back on once the car goes through the evap system pressure check again.

No real harm done IMO.