New tools for DIY car diagnosis

This post comes from Brandon Ballenger at partner site Money Talks News.

How can you tell if your mechanic is playing it straight or taking you for a ride?

Most of us can't because we aren't car experts. A 2007 survey by GLG Research indicated that 70% of consumers don't even change their own oil. And if the "check engine" light comes on? Forget it. 

New hand-held diagnostic devices can help back up or challenge what your mechanic says about some repairs. In the video below, Stacy Johnson gives one called CarMD a try. Check it out, and then read on for more.

As you saw, the tool was right on the problem, but wrong on the fix. According to the mechanic, Stacy's check engine light came on due to a failure of an air pump that's part of his car's emission control system, exactly as CarMD said. The fix it suggested, however -- replacing both the pump and pump relay at a cost of more than $1,000 -- was probably wrong.

"It's highly unlikely you'll need those expensive parts. It could be something as simple as a loose wire," the mechanic said. "There's no way this simple scanner can possibly know what's wrong in detail."

In short, like WebMD for health issues, CarMD might be helpful with identifying symptoms, but you shouldn't rely on it to tell you exactly what's wrong or how much it will cost to fix. You'll still need to talk to, and rely on, a professional.

Here's what you can do:

• You buy or borrow the tool. If you purchase CarMD straight through its website, it's $120 plus shipping. They also have a return policy that promises a refund (minus shipping) if the product doesn't save you three times its value in a year, but it's not valid if you buy it from a third party or reseller like Amazon, eBay, or your local warehouse store, where the price may be cheaper. If you have more than one car, no problem: The same device can be used for multiple cars. Also keep in mind that some auto parts stores offer free diagnostic service, so it may not be necessary to buy it at all.
• Plug the device in. When the check engine light comes on, you plug the CarMD into your OBD (on-board diagnostic) port, which may be in any of several locations depending on your make and model, including beneath the steering wheel and under the passenger-side dashboard. If you can't find it, CarMD's site can help. Every car made since 1996 should have one.
• Take it to your computer. Once the tool has downloaded information from your car's computer, plug it into your computer using the included USB cable. It'll take you online to check any error codes your car reported against CarMD's database and try to guess the issue. Then it will estimate the cost of parts and labor to fix the problem.

CarCheckup is a similar tool that can also be used to graph road trips and track business mileage or driving habits for $150. CarChip provides those functions for $100. These tools may also be useful for checking out used cars before you buy.

While checking diagnostics is simple enough, there is no replacement for a trained and trustworthy mechanic. But if you insist on skirting the auto shop for a little while longer, you might try Car Talk. They help diagnose car noises, offer do-it-yourself instructions for simple auto repairs, provide tons of information, and have both a forum and a well-known radio show on NPR where you can ask for help, not to mention a searchable list of user-reviewed mechanics. Edmunds.com is another good place for car and maintenance advice.

More on Money Talks News and MSN Money:

• Do gas saving devices work?
• The 4 best ways to improve mileage
• 7 ways to save on car insurance
• Repair the car or spend the cash?
• The most and least expensive cars to insure
• Make your car last 250,000 miles