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Computer Codes Engine Check

I went to Auto Zone to get a free engine diagnostic to see what the code was for my Engine Malfunction Light. But the Honda Dealer wanted to charge me 95 bucks for the same thing. Why? What does the dealer do that Auto Zone does not do? (steal my money is not an answer)

All that Auto Zone does is plugs a code reader into your car and tries to sell you parts to throw at the car to try to make the light go away. For example, Auto Zone’s counter person may scan your trouble codes and receive a code P0131, which has a generic definition of “O2 sensor circuit low voltage bank 1 sensor 1”. They will then tell you that this code means you need an oxygen sensor. They will then try to sell you a new oxygen sensor and probably the tools to replace it. You will then go home and install the new oxygen sensor, return to Auto Zone to have the code cleared, and probably end up with the same code once again within a couple days and still end up having to take your car somewhere to have a real diagnosis done and have the real problem corrected. Auto Zone’s “free diagnosis” is one of the worst misnomers around and is nothing more than a sales tactic, a method of moving more parts.

The dealership (or any good repair shop) will read the codes and use further diagnostic methods (flow charts, circuit testing, etc) to pinpoint the exact cause of the trouble code. This can often take an hour or more to do properly. Many times, the diagnostic fee will be waived if you authorize the repairs. As I indicated earlier, a real diagnosis is much more likely to actually solve your problem and leave you satisfied with the results, and you may actually save money by not going with Auto Zone’s “free diagnosis” if they end up unloading some expensive parts on you. One of their favorite parts to move is a mass airflow sensor. Any code they pull relating to air or fuel is often “diagnosed” by them as a failed mass airflow sensor. Why? The part is easily replaced by the average consumer, and it is very expensive. It makes them a lot of money, whether it solves the problem or not. Also, many mass airflow issues can be solved by a good cleaning with a $4 can of mass airflow cleaner.

The AutoZone guy is making X dollars an hour to sell parts. The time spent pulling codes is just part of his daily job. He’s making X dollars a day no matter what and AZ is making a profit on parts sold.

The mechanic at the dealer works on flat rate and is part of the service department which does not sell parts, except indirectly. The parts dept. is essentially a separate entity at the dealer.
If the mechanic at the dealer did not get paid a flat rate charge then in all honesty he would starve to death quickly.
It would be easy for a mechanic to pull codes all day long and go home that evening without earning one single dime. (Guys who have turned wrenches for a living know how that works all too well.)

The business model is completely different and one simply cannot compare the two.

I don’t mean to restate what’s been said, but if you’re the kind of person who goes to a parts store instead of a mechanic to address a check engine light, it’s in AutoZone’s interest for you to know the code (so they can sell you a solution).

Before I bought my scanner, I went to AZ to get a code read and I found the help to be quite competent. They gave me a print-out of likely fixes and started by recommending the cheapest possible fixes (fuel injector cleaner and MAF cleaner for a lean code). I ended up buying a scanner and finding that the MAF gave abnormal readings. I replaced it and that finally fixed it. If they’d started out by suggesting an $85 part, I would have run away. But they suggested the cheapest things first. They ended up making a decent sale on a service that takes only a few minutes, and I spent a whole lot less than a garage would charge. We both win.

As a direct answer to your question, the dealer may have access to software that is not available to others. This might help when there’s a difficult to diagnose problem. But in most cases the generic code that any code reader can give will point you in the right direction. A mechanic can also look at other information and make an actual diagnosis. The AutoZone service is limited to reading codes and suggesting possible fixes.

thanks… yes it is a money world on both sides.

thanks… yes it is a money world on both sides.


Not to beat a dead horse, but autozone can only give you any stored generic codes. They do make the standard recommendations, the same ones found on or other similar websites. This good for many of us who have worked on our own cars for many years.

You can go this route if you like, then post back the code, not the recommendations but the code itself here along with the make, model, year, engine/transmission info and you may get some insight that you will not get from Autozone.

The dealer can not only access the generic codes, but also Honda specific codes that Autozone won’t see. These might help pinpoint the problem. In addition, the service manual that the dealers mechanic is using has troubleshooting procedures to further isolate the problem and give you a more accurate diagnosis. At the dealer, you are not paying for pulling the code, you are paying a diagnostic fee.

Try Autozone first and post here. If you are not comfortable with the results, then use the dealer.

p0404 — EGR Flwe CKT range/performance

flow not flwe

My somewhat limited experience is even if you have read the code at home for free, most mechanics want to read it again at full dollar charge. In part this makes sense, since they are expected usually to guarantee their work. In part, as we have seen on this board over the years, they also assume the stupid car owner has no idea what he is doing.

Several years ago, I had a code indicating a problem in the evap system on my 2002 Sienna. It was very intermittent, and I knew from my own career with high tech electronics that intermittents get very expensive. So, I kept monitoring it with my own scanner. At one time it went several months without a failure.

Finally, a man on the now defunct Sienna Club forum said he had two Sienna’s and one had the exact problem. He swapped parts, and found it was the charcoal canister. There are allegedly low pressure valves on there, and his guess is one got sticky.

I took it to the dealer in McAllen, and told him I was taking responsibility for the diagnosis and did not want to pay for re-troubleshooting an intermittent they most likely would never see in the shop, anyway. He had me sign a warranty waiver, and they replaced the canister. It has worked perfectly for several years since.

In the 70’s I was working on an area navigation computer. We got one back from the customer with an intermittent problem. I knew by the symptom exactly what caused it. The woman tech, a personal friend since we were kids, said she had to see the failure herself, which is nonsense. She ran and asked Gomer Pyle, er, I mean our boss who said, yes, if you don’t see it, don’t do anything.

So,she wasted the customer’s thousand plus dollar cost sending it back, as well as put the airplane at risk with a unit that had a known failure, and could easily have been fixed, since there was only one component that could cause that precise failure.