Should I go to a dealer or an independent shop for engine diagnostics?

Use the dealer when the car may be under warranty, when the problem looks like a recall, or when it is a fault specific to your make. Use a good independent shop for most other engine diagnostics. Neither choice costs you your rights: Virginia's repair law applies to both, and federal warranty law limits what a manufacturer can require.

When the dealer makes sense

• The car is under warranty. If the repair might be covered, check the warranty terms in your booklet before paying anyone, since covered work may not cost you anything.
• It may be a recall. Ask the dealer whether any open recall applies to your car.
• It is a known fault for your model. Dealers work on one brand all day, so they may recognize a pattern quickly. Ask what they have seen.
• Your car needs manufacturer software or tools. Some newer systems can only be fully tested with them. Ask an independent shop whether it has what your car needs rather than assuming either way.

When an independent shop makes sense

• The warranty has expired. There is little reason to pay for the brand name alone.
• You want a relationship. A shop that knows your car's history can spot a pattern.
• You want to compare. Independent shops are easier to get a second opinion from, and a written diagnosis lets you shop the repair.

What the law says

Virginia's Automobile Repair Facilities Act applies to any person who for profit diagnoses or corrects malfunctions of, or damage to, a motor vehicle.^[1] A dealer and a corner garage are held to the same rules:

• A shop may charge a reasonable fee for the estimate and related diagnostic work, but must disclose the condition when you ask, in writing or on a sign posted at the entrance.^[2]
• On request, before any repair work for which you may be charged more than $25, the shop must give you a written statement of the estimated labor, the estimated parts, a description of the problem or work and the estimated completion time.^[2]
• The shop cannot charge more than 10 percent over the written estimate, or 20 percent for a vehicle at least 25 model years old, unless you authorize the extra work or time.^[2]

Warranty work is also paperwork. The invoice must be provided for work performed under a warranty too, and must separately identify parts provided under warranty and not under warranty.^[3]

Will an independent shop void the warranty?

This is the usual worry, and federal law speaks to it. Under federal law, a warrantor of a consumer product may not condition its written or implied warranty on your using a service identified by brand, trade or corporate name, unless the Federal Trade Commission grants a waiver.^[4]

In practice, keep your service records and invoices. If a warranty claim is ever disputed, they show what was done and when. Read the booklet for any maintenance it requires.

How to choose

Call two or three shops, including the dealer if the car might be covered. Give each the same description of the problem and ask the same questions: the diagnostic fee, what it covers, whether it is credited to the repair, and who will work on the car.

Then compare written estimates, not phone quotes. The cheapest diagnostic fee is not the best deal if it only reads a code and leaves you to pay again for the testing.

Stop and call a pro if

• The car overheats or loses oil pressure. Stop driving and have it towed to whichever shop you choose.
• A shop will not put the estimate in writing. You can request one, so take the car elsewhere if it refuses.

Getting help in Virginia

For what a diagnosis costs, see how much a car diagnostic test costs in Virginia. Browse more automotive repair answers or automotive repair businesses.

To compare local shops for your own vehicle, describe the problem once and shops will respond.