In an age of self-piloting cars and computerized features, many things can still go wrong with your car. That means drivers still rely on human mechanics to keep their rides rolling. Unfortunately, the nonprofit Twin Cities Consumers' Checkbook finds many repair shops disappoint their customers: they do lousy work, impose long delays, sell unnecessary repairs, give inaccurate estimates.

But not all shops are lemons: Plenty almost always perform top-quality work quickly and for a fair price.

Checkbook's evaluations of 308 shops in the Twin Cities area include its ratings for quality and price. Its ratings are based on more than 8,000 reviews by local consumers, consumer agency complaint records, more than 1,200 price checks by its undercover shoppers, and other sources.

For the next month, Checkbook is offering free access to its ratings of area auto repair shops to StarTribune readers via this link: Checkbook.org/StarTribune/AutoRepair.

Fortunately, there are a lot of top-quality auto repair shops in the area. Checkbook found that 118 of the shops were rated "superior" overall by 90 percent or more of their surveyed customers. But there are plenty of shops to steer clear of: 38 got such favorable ratings from fewer than 60 percent of their surveyed customers.

Checkbook's ratings of area shops include a separate rating for price, derived from price quotes collected by its undercover shoppers for several carefully constructed repair jobs. You want to be sure a shop charges fair prices before you bring in your car because, as with most repair work, it is difficult to shop for price before you know exactly what needs to be done.

Checkbook's undercover shoppers found dramatic shop-to-shop price differences. For example, to replace the water pump for a 2011 Ford Escape XLT, they were quoted prices by area shops ranging from $189 to $560. Hourly labor rates ranged from $70 to $161.

If you know what repairs you need, you can compare prices from shop to shop on your own by calling a handful for quotes.

If you don't know what work is needed, call one or more shops and describe the symptoms — what the car is doing or not doing. Shops might be able to tell you over the phone what's likely to be wrong and quote a price. If so, get quotes from several shops.

When shops can't determine what's wrong with your car based on your description, you will have to take it in for a diagnosis and estimate. Then, with estimate in hand — and assuming that the diagnosis is correct — check with other shops to see whether the shop's price is fair.

You don't have to pay more for good service: Checkbook found many top-quality, low-price shops in the area.

Many consumers believe dealers offer better repair service due to access to sophisticated diagnostic software, and high-tech tools, not available at independent garages. That's not true. In fact, Checkbook found the opposite: On average, shops operated by non-dealers were far more likely to satisfy their customers than dealerships — and offered far lower prices. The non-dealers were rated "superior" overall by an average of 85 percent of their surveyed customers compared to only 68 percent for dealers. Prices at non-dealers averaged about 10 percent lower.

Both dealers and non-dealers subscribe to the same databases that provide repair instructions, diagrams and news from manufacturers. Independents have access to the same tools and equipment.

Checkbook's advice: If the work you need is not covered by a new-car warranty, use an independent shop.

With any shop, communication is critical. Checkbook advises:

• Give the shop a detailed written description of your car's symptoms. But distinguish between what you know and what you think you know. If you know what needs to be repaired, tell the shop, but don't guess. If you mention a specific problem — say, a bad alternator — the shop may replace a perfectly good alternator (and charge you for it), before fixing what is actually wrong.

• If possible, speak with the repair technician who will be working on your car. Service write-up personnel at large shops often know very little about car repair, and those who do know car repair may not be able to describe your car's symptoms to a repair technician as well as you can.

• Either get a written estimate in advance, or write on the repair ticket that no work is to be done without your approval.

• Get a written, dated invoice that details charges for parts and labor, and the vehicle's odometer reading.

• Pay by credit card — you can dispute the charges if things go wrong and the shop isn't responsive.

• If the car is still not right when you get it back, immediately inform the shop, preferably in writing.

Twin Cities Consumers' Checkbook magazine and Checkbook.org is a nonprofit organization with a mission to help consumers get the best service and lowest prices. We are supported by consumers and take no money from the service providers we evaluate. See ratings of area auto repair shops free of charge until Oct. 5 at Checkbook.org/startribune/autorepair.