Last updateWed, 20 Sep 2017 9am

On The Road

Seeing the light on low-cost check-engine diagnostics

Q: Can you explain why there are so many ads out there that offer an array of prices – some even free – for check-engine-light diagnostics? How important is it to bring your car to a shop when the light comes on?

A: The check-engine light performs an important service and should not be ignored. It tells you there is something out of sync within your car’s emissions system that needs to be addressed. If your check-engine light is on when you try to renew your smog certificate, your car will automatically the fail the test.

The service to diagnose why your check-engine light is on can only be performed correctly if the shop has invested in the right equipment, the right software and trained technicians with access to the right information to determine the cause of the warning light.

Equipment and software must be updated annually – at great expense to the shop owner. Technicians must undergo training, at least 40 hours per year to gain the knowledge required to interpret the information accumulated from the diagnostic equipment. The information is available at an ongoing expense paid by the shop to manufacturers, on-call services and aftermarket online services.

The only information provided by the vehicle’s control unit is an error code with a definition, which only points to a vehicle’s particular system. The technician must then determine which component or components within the system have malfunctioned. The repair can only take place after this step is accomplished. Anyone without the knowledge and equipment is just guessing at the correct repair. The danger of such guesswork is that if the cause of the warning light is not repaired correctly, additional damage may occur to other components in the vehicle.

Make sure the facility you take your car to has the ability to do the job correctly. If the first step in the process – determining why the light came on – is free of charge or there is a minimal charge, it usually means that there has been no investment in the correct equipment, software or training, and the outcome of any subsequent repair may not be what you expect. Sometimes the code is pulled, but then you are asked to spend more money to examine what prompted it.

Even worse is when the code is pulled and a diagnosis is reached, but the diagnosis is wrong because of lack of knowledge and correct equipment.

Those who think they are saving money by responding to an ad for an inexpensive check-engine light may end up with more problems.

Warren McCord is an ASE certified master technician and owner of Dean’s Automotive Inc. in Mountain View. For more information, call 961-0302 or email McCord at This email address is being protected from spambots. You need JavaScript enabled to view it..

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