car diagnostic test what does it cost

Car Diagnostic Test: What Does It Tell You And How Much Does it Cost?

Your check engine light comes on, and you find out you need a car diagnostic test. What is it, how much does it cost, and where can you get one? Find out these answers and more below.

Further, if your car ends up needing an expensive repair, we’ll reveal four affordable financing options that can help.

Let’s get started.

How does a car diagnostic test work?

To understand, it helps to gain a little background knowledge.


In 1996, the Environmental Protection Agency (EPA) mandated that the computer interfaces for all vehicles in the U.S. meet the same common standard: the On-Board Diagnostics, version 2 (OBD II). As a result, all auto repair shops only need one tool to run scans on all vehicles.

Computerized vehicles

The majority of modern fuel-injected vehicles have automatic transmissions, fuel injection systems, and ignition systems that are controlled by computers. The computers continuously receive data from dozens of sensors within vehicles to optimize the combustion process. This helps to ensure good gas mileage, power, and low pollution (which explains the EPA’s involvement).

The system continuously monitors itself and makes adjustments. If a sensor sends data to the powertrain control module (PCM) that doesn’t make sense, the check-engine light will come on, and a trouble code will be stored. The vehicle will try and compensate for the problem, but the driver needs to get it checked as soon as possible. How does one do that?

Car diagnostic tool

This is where the car diagnostic machine comes in. A technician will plug the scanner into your car’s standard OBD II connector, enter information about your vehicle (VIN, engine type, etc.), and perform the scan. Afterwards, they will get a full report containing the trouble codes.

Car diagnostic codes

The codes consist of one letter and four numbers (i.e., P0100).

DTC Structure check engine

  • The letter can be a “P” for powertrain, “B” for the body, “C” for chassis, or “U” for undefined.
  • The first number will either be a zero (which means it is a generic code shared by all manufacturers) or a one (which means it is a manufacturer-specific code).
  • The second number will be a number from one to eight, and it specifies the area of the problem.
  • The last two numbers identify, more specifically, which section of the system is malfunctioning.

By reading the codes, the technician can identify the area and system that is malfunctioning.

Identifying the problem

“A good diagnostic test will inform you how long the issue has been present, both in real-time, key/start cycles, and drive cycles, while also telling you how many times this error has occurred during that time. This tells you if the problem was a fluke or if you have a degrading system as a whole that will need to be addressed,” says Matt Barton of The Hero Labs.

He adds, “The law of the land basically states that an OEM manufacturer is only legally required to activate a check engine light when a component or system test fails in such a way that it causes the vehicle to fail emission standards. This means you could potentially have problems that won’t illuminate a check engine light.”

With this in mind, it’s not a bad idea to get a checkup periodically.

How much does a car diagnostic cost?

“Typically, it should only cost one hour of shop rate time (the amount a given shop charges for their hourly rate). It varies by region and is usually somewhere in the ballpark of $65 to $100 per hour,” says Barton.

RepairPal reports that a car diagnostic test costs between $88 and $111 before taxes and Popular Mechanic says it can cost from $20 to $400.

As with any financial decision, it’s smart to check at least three places.

Can you get a free car diagnosis?

Barton says, “As a mechanic and small business owner, my job is to make money, so I always include a free check with service for the potential up-sale on my end. Many places will do this if you just ask, and hey, a free check never hurt.”

He adds, “Unfortunately, there are some very pushy service writers and shop owners who may try to sell the problems found as catastrophic, and convince you that you need to spend a ton of money as soon as possible. Most times this isn’t the case, so make sure you go to a reputable establishment that you can trust.

In the rare case you come across this situation, ask them the same questions you would ask your doctor: How bad is this? Does it have to be addressed immediately? Are there any other causes of this problem? Lastly, if you’re unsure, always get a second opinion.”

Find a car diagnostic test near me

Every auto repair shop should have one of these scanners. However, it’s important to choose your mechanic wisely. The tool can show the problem codes but doesn’t always tell why something is occurring.

Identifying and efficiently fixing the problem will depend on the experience and skill of the mechanic. Further, as Barton points out above, integrity can also be an issue. Be sure to go to someone you trust, or who comes highly recommended.

4 ways to pay for an expensive repair

If you end up needing an expensive repair and don’t have the funds to pay for it out-of-pocket, here’s a quick list of financing options to consider.

1. Get a personal loan online

Getting an unsecured personal loan is one of the easiest ways to borrow cash fast. Apply online and, upon approval, have the money in your bank account in as little as one day. Look for low interest rates, minimal fees, and good customer service.

Browse personal loans and compare top lenders. 

With SuperMoney, you can use our personal loan engine to get personalized offers from dozens of lenders competing for your business. Get your rates without hurting your credit

2. Borrow from friends or family

Consider asking a friend or family member if you can borrow the money. By doing so, you can usually pay less than you would pay to an official lender and you won’t need to pass a credit check. The downside? Your relationship is securing the loan, so if something goes wrong, it could cause a rift in your personal life.

3. 401(k) loan

If you have a 401(k) retirement account, you may be able to take out a loan against a percentage of your funds. The interest rate is typically low, and the repayments will often come out of your paycheck before you receive it.

If your credit score is in the poor-to-fair range, this option is attractive because a credit check is not usually required. However, if you don’t keep up with your regular 401k contributions, your retirement savings will take a hit.

4. Credit card with no interest offer

Lastly, consider a credit card with a no-interest introductory period. During the promotional period, you will pay no interest on your balance. If you use it to pay for car repairs, you will have time to pay it off before the interest kicks in.

Shop and compare credit cards here.

The catch is when the promotion ends, the interest rate jumps up and can be very expensive, so you’ll need to pay it off in time. Further, you’ll have to get approved based on your credit score.

Read about more quick ways to borrow money.

Get your car back on the road

Even though a car diagnostic test can bring bad news, the sooner you find out about a problem, the better. Otherwise, one problem can quickly turn into many more.

The scan itself should be around $100, but depending on the problem and the mechanic you hire, getting to the root of the problem can cost more. If you do end up needing financial assistance, try one of the four affordable options above.

Find out what rates you can get on a personal loan now