The cheapest way to diagnose your car's check engine light

auto service, repair, maintenance and people concept - mechanic men with wrench repairing car at workshop
auto service, repair, maintenance and people concept - mechanic men with wrench repairing car at workshop

HOUSTON – That dreaded check engine light on your car's dash could signal you need major repairs or something as simple as a new gas cap, but you don't want to spend a lot of time or money figuring out what's wrong. 

Consumer expert Amy Davis bought a personal code reader at Fry's Electronics for $19.99. The Micro Mechanic plugs into your car and wirelessly connects to your smartphone to tell you what's wrong.

We tested it on Channel 2 promotions producer Mariah Gardner's 2005 Acura. Gardner's check engine light lit up about 3 weeks ago. She took it to the shop for a diagnosis but asked the mechanic not to clear the code or light check engine light so we could see how the Micro Mechanic would work. 

The small device plugs into your vehicle's port. When you download an app on your phone, it wirelessly displays the diagnosis on your screen. 

"And it's saying 'No problems found. Safe to drive," Gardner said.  

That was the readout on the Micro Mechanic app, even as Gardner's check engine light glowed. 

"My mechanic would beg to differ," Gardner told Davis.  

Gardner downloaded another app recommended in the instructions that come with the Micro Mechanic, but it would not connect with the device at all. 

Finally, the third app she tried gave her some information. It gave her 3 trouble codes: the evaporative emission system low purge flow, evaporative emission system leak detected (that could be a loose gas cap) and the catalyst system efficiency below threshold. 

"I wouldn't really know what to do with this," said Gardner. "It doesn't tell you how severe it is. It just tells you what the code is and what that reads."
A mechanic did tell Gardner the exact same things. The codes from the app and the invoice from the mechanic even match, but the technician took it a step further and let her know she can safely hold off on the pricey repair. 

"It really is something I should get fixed,: Gardner told Davis. "It's just not life-threatening." 

Next, Gardner drove her car to O'Reilly Auto Parts. It's just one of many auto parts chains that will diagnose your check engine light for free. In minutes, an O'Reilly employee gave her the same codes, along with 10 others, for a total of 13 problems detected. But the employee couldn't elaborate on any of them or print them out for Gardner. As a customer, she would have left just as confused as when she came in.  

The bottom line is you are likely going to need a mechanic regardless to make repairs. But you can always use O'Reilly or one of the personal code readers to confirm what your mechanic is already telling you. If you notice a big discrepancy in the diagnosis, that's when you should go to another repair shop for another opinion.