Mechanic checking codes from OBD2 scanner

If you’re dealing with car troubles, you might be wondering, “How accurate are OBD2 scanners? Are they worth using to diagnose my vehicle’s issue?” Our cars are more and more controlled by computers, sensors, motherboards, and CPUs. This has brought great benefits to car ownership – what would we do without adaptive cruise control and automatic emergency braking? – but makes the diagnosis of common ailments harder than ever. Thankfully, an OBD2 scanner can make automotive troubleshooting a little easier.

Despite their name, this isn’t some distant cousin to R2-D2. OBD2 scanners are invaluable tools for anyone trying to do DIY repairs on cars built in this millennia. With the increasing digitization of the automobile, these scanners are quickly becoming a must-have for the enthused car owner.

These days, there are a number of OBD2 scanners on the market across all price points. But how accurate are they devices? Are they really worth the hype, especially since the chain auto parts stores often offer a free diagnosis?

We wanted to learn more, so we took a dive into the world of OBD2 scanners to really find out how accurate these tools really are. But before we get into that, we should go over what these tools are and what they are designed to do.

What is an OBD2 Scanner?

Woman using OBD2 scanner

The acronym OBD2 stands for on-board diagnostics, second generation. It is a system used on all cars and trucks that was designed to provide an easy diagnosis of certain failed parts, such as sensors and emissions equipment. The idea was that the part would fail, a check engine light would come on, and a code pertaining to the failure would be stored within the car’s onboard computers.

This is where the OBD2 scanner comes in. The scanners plug directly into the car via a connector found in the cavity just above the pedal area. The scanner can pick up the code stored by the onboard computer. Using that code, a technician can begin to determine exactly what repairs are in order.1

OBD2 debuted in 1996 on all cars and trucks sold in the USA. Twenty-five years on, it remains the universal standard for automotive onboard diagnostics.2

How Accurate Are OBD2 Scanners?

Entirely accurate. These devices are not rocket science, and nor are they pocket mechanics. They simply report out the codes they extract from the car’s computers.

Where things get tricky is when it comes to interpreting the codes. Codes may look straightforward, but replacing the obvious culprit may not alleviate the condition. For instance: code P0457 translates to “Evaporative Emission System Leak Detected (Fuel Cap Loose/Off).”3

Typically, this points to a gas cap that isn’t entirely screwed on or has otherwise begun to improperly vent fumes. Either issue seems easy enough of a fix: tighten the cap or otherwise buy a new one. But what if the code comes up even with a new cap?

Your first reaction might be to blame the scanner. But the scanner is doing its job perfectly: it is just the messenger, relaying the code initially determined by the car’s computers. If the OBD2 scanner was still picking up code P0457 after you replaced the gas cap, it means the condition that first caused the code to begin hasn’t been resolved.

At this point, a seasoned mechanic might check the fuel filler tube, which can grow brittle and begin to vent out gas fumes – and throw the same code suggesting to replace your gas cap. But the scanner won’t allude to any of this. It only points in the direction you should begin your diagnosis.

Are Some Scanners More Accurate Than Others?

Mechanic using OBD2 scanner for diagnostics

There is a raft of scanners on the market, from cheap Bluetooth accessories that work from an app on your phone to four-figure devices that offer enough functions and data to make your head spin. Fortunately, they’re universal, so any OBD2 scanner will work for a vehicle manufactured after 1996. However, it’s fair to wonder if they all adhere to the same standard of accuracy.

The answer is yes – these devices are all accurate. If a code is present, they’ll pick it up and relay it back. However, that doesn’t mean the $455 Snap-On scanner is suddenly on par with your $40 Auto Zone special. As the price goes up, features, functions, usability, and convenience all improve substantially.

All OBD2 scanners fall into one of two camps: plain code readers and more advanced scan tools.

Code Readers

Code readers are limited in function and affordable in price. A typical example of a code reader is an entry-level Bluetooth scanner. These little wireless devices plug into your OBD2 port and wirelessly transmit the results back to your smartphone. For the average car owner who wants to keep tabs on their car’s diagnostics, this is the most cost-effective and convenient option.

There are other code readers as well, including some that are handheld units with wired cords that plug directly into the OBD2 port. The level of data that can be retrieved beyond error codes varies by price point, but typically you can at least see general dashboard metrics such as oil pressure and transmission temperature.

Some code readers may also allow you to clear codes. You might think you’re cheating the system if you do this prior to your emissions test, but clearing the code is only temporary at best. Whatever condition caused the code still persists, and within 100 miles or so – the computer needs a few drive cycles after being cleared before it again alerts you of codes – your check engine light will return.

Scan Tools

For when you really want to crunch data, you need a scan tool. Mechanics, enthusiasts, race teams, and other professionals all turn to these highly advanced, multi-functional tools for not only picking up trouble codes but for in-depth performance analysis and even ECU tuning and other modifications. These tools can cost hundreds or even thousands of dollars, but they offer unparalleled functionality.

Parting Thoughts

There is all manner of OBD2 scanners on the market, but despite the breadth of choice, there is little reason to doubt the accuracy of even the cheapest offerings. As long as the connection to the OBD2 port is sound, these devices should honestly pick up whatever codes your car may be storing.

The key is knowing what to do with the information provided by the scan tool. Scanners can point the way when the only thing wrong is the check engine light, but they’ll never lead you to a solution. That takes traditional diagnosis.

An OBD2 scanner alone won’t turn you into a DIY master, but they can help you up your game considerably. If you want to arm yourself against a future check engine light, check out our article on the best OBD2 scanners.

Article Sources

Ride Digest uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. Brewer C. How To Use An OBD2 Scanner. Carfax.com. Published July 31, 2020. Accessed July 21, 2021.
  2. L M. What Year Did OBD2 Start? Here’s A Brief History Lesson. Scanneranswers.com. Published January 25, 2020. Accessed July 21, 2021.
  3. Repair Pal. P0457 OBD-II: Evaporative Emission System Leak Detected (fuel cap loose/off). Repairpal.com. Accessed July 21, 2021.