J M Mechanical - Automotive, Truck & RV Repair and Service in Canby, Oregon

Why do some parts stores and shops read codes for free?

It is fairly simple to "read" the codes in a cars computer. These codes are set anytime the computer detects a problem with itself, one of its sensors, circuits, commands, etc. Anyone with a $45 code reading tool can access that information. Often the code will relate to a specific component or components. Some parts stores have been doing this as a way to get customers to come in and buy parts from them, and often times electrical parts are not returnable once opened or installed. If the code was for a mass airflow sensor and you bought one and installed it, you now own it - regardless of whether it fixed the problem or not. Some shops offer this service for free, but be careful; they may increase charges in parts and labor to your bill to offset giving away this service.

So if it's so easy to read codes, why do you charge a diagnostic fee?

There is much more to a diagnosis than simply reading codes. That's just the first step of many. After code reading we take the car on a road test, usually with a scan tool connected and recording data from the cars computer. We then use that data along with the code to zero in on the suspect area, followed by pinpoint testing of the affected component or circuit. A check for service bulletins will also occur at this time to make sure it isn't a common problem or one that might be fixed for free under a recall. After replacing a failed component or making a repair we then clear the codes and re-road test the car to be sure the problem has been properly diagnosed. Not only is this much more time consuming than just reading codes, it also requires highly trained technicians and the $45 code reader is replaced with a $3500 (or more) scan tool, service information system, digital storage oscilloscope and various other test equipment.

A 2001 Toyota Corolla came in with a check engine light on, and the owner noticed no problems with how the car ran. The codes were retrieved and the car had a P0420 stored, which technically is "Catalyst efficiency low bank 1" and in English means the catalytic converter (part of the exhaust / emissions system) is no longer doing its job to reduce emissions. Had we simply replaced the catalytic converter the light would have come back on in just a short period of time. During testing it was noted that the catalyst was behaving in a normal manner, and in checking with the engines computer it showed it had passed its last self test. During extensive road testing it was found that the rear oxygen sensor would intermittently drop in and out of operation, causing the cars computer to believe there was a problem with the catalytic converter when all along the problem was with a completely different component. Had we replaced the catalytic converter the cars computer claimed had failed we would have replaced a very expensive part that was still doing its job just fine. Proper diagnosis of the problem led us to the real culprit, which happened to be a much cheaper repair and kept the check engine light from coming back on.

So the bottom line is, you get what you pay for!

Yes, it is possible that a car can be properly repaired without paying for diagnosis, but we usually find that is the exception, not the rule. As noted before, a code may not relate to a specific component, or there may be a problem with the wiring, not the part itself. Occasionally a cars computer develops a problem and may start to blame other parts for its own failures. Without spending the time (and money) to fully diagnose a problem you may find yourself paying a lot more in parts and repairs than had it been checked properly in the first place!

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