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New tools for DIY car diagnosis

Your mechanic sounds sympathetic as he explains that you need an $800 repair. Should you believe him? New computer diagnostic tools can help you decide.

By Stacy Johnson Aug 2, 2011 9:20AM

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. is another good place for car and maintenance advice.

More on Money Talks News and MSN Money:

Aug 4, 2011 9:06PM
Diagnostic tools are only as good as the person interpreting the results.  A tool like this CarMD will not save you significant money unless you're already taking a drubbing every time that you go to a mechanic, and as has been mentioned here, most mechanics really are honest.  I'll offer an example of a recent problem I had with my F-150.  When considered in comparison to the generic misdiagnosis that the CarMD gave in the article, I think it shows that the scanner itself does not save a person money unless that same person can also make their own deduction as to how to rectify it. 

The engine light came on, and the diagnostic code displayed that the engine was missing intermittently on the fourth and seventh cylinder.  This could have been caused by a myriad of problems.  The reality though, available through some simple deduction, is that this year F-150 has two ignition coils and the 4/7 connections are both on one side of one of the coils.  So, you see, the computer stated what the problem was, but it required some mechanical deduction to guarantee that the correct part was replaced.

Aug 4, 2011 4:44PM
So this would have been a more informative article if you had let us in on what was actually the problem. Did you have to replace the relay, the pump, or both? Loose wires, etc.?
Aug 4, 2011 3:04PM
Right on Micheal!  I've been a mechanic 40+ years.  I've seen the industry go up and down.  We are just the same as any other American worker.  The mid 80's to the mid 90's were the most profitable.  The late 60's was the most fun and profitable.  Unfortunately we have been hit hard with financial problems in America as well.  I have made a decent living being honest, I have also worked with thieves and hacks that many shops and dealerships tolerate due to the income they provide.  From my experience the vast majority of mechanics are honest.  We also have been over run by the greedy corporations and/or owners.  My yearly income has dropped an average of $10k a year.  So please do not blame mechanics for vehicle costs of repairs or parts.  These greed focused corps/owners find every way possible to make more profit for themselves everyday, even if it means screwing the employee.  Sound familiar?  Concerning the carMD,  sounds like an advanced hand held code reader with some percentage based fixes.  These tools will get you in the ballpark but definitely are not going to be always accurate on fixes.  Many vehicles will set the check engine or service engine soon lights designating computer controlled systems that are out of normal operating parameters which are preset in the computer by engineers.  Mistakes happen.  Corroded connections occur, rodents, rabbits and many other creatures cause problems chewing up wires.  Splices in factory wiring harnesses, corrode and are located somewhere in the wrapped up harness.  Mechanics usually know how to diagnose better than a machine.  There are many variables in vehicles and many times a code set is not related to the problem.  The problem may be causing another system to fail and not be a failed system itself yet.  The labor times set by shops is also been going down also.  As Micheal stated most mechanics work on commission, thus the employer pays you nothing if you aren't working.  By lowering the labor times and raising the flat rate per hour charged to customers the shop gets more money and the mechanic gets less.  For example a shop charges $100 per hour.  The top mechanic gets $20 per hour.  The next week the same job pays the mechanic .8 of an hour and they raise the shop rate to $110.   Now the mechanic gets $16 and the shop gets $94.  Personally I call this the extortion of the American workers!   carMD will most likely give a little more confidence to the consumer if they already know which system is causing the light to come on before taking their vehicle to a shop. Just remember, your mechanic is also under a lot of stress.     Many bosses expect more miracles than possible everyday.  The Rockefeller complex, more is never enough.  And one very important thing I almost missed,  DO NOT let the auto parts store touch your cars computer!!!  They are in the business of selling parts, not repairs.  I have seen many times valuable information erased by the parts store which can cause a more time consuming diagnosis. 
Aug 4, 2011 1:18PM
all that is, is a code reader not a scanner. a scanner can let you see where the problems developes. if its a hard set code or a intermittant code. a code reader just tells you what code the on-board computer seen and it could be just a intermittant problem due to a broken wire or loose connection.
Aug 4, 2011 1:08PM
its not us mechanics that do the recommendations. its the shops service writer. we just diagnos the customers complaint and tell the service writer what we found. people always blames the mechanics for what they have to pay, we dont set the labor price, the greedy owner of the shop does. back before greed took play in society, it use to be 50/50 on pay, now its hard to get a shop to pay us at least a 25 dollar flag hour wage. shops now only want to pay a 15 dollar flag hour. thus meaning if the job is said to pay 1.0 hr we get 15 dollars for that.  shops also do a mark up on the parts that will fix the problem. 50% mark up at most, and some shops arent honest to thier customers either. your 300 dollar alternator may cost the shop 150.
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