Updated on Sep. 13, 2024
A glowing check engine light (CEL) usually means your vehicle has a problem. A scan tool or code reader can help you identify the problem yourself.
Our editors and experts handpick every product we feature. We may earn a commission from your purchases.Learn more.
In 1996, On-Board Diagnostics/2nd Generation (OBD-II) diagnostic systems became standard on all vehicles. OBD-II identifies problems with the drivetrain and other mechanical or electrical components and systems, making driving safer and more pleasurable.
Specifically, OBD-II generates diagnostic trouble codes (DTC) and activates the check engine light (CEL), malfunction indicator lamp (MIL) or other warning lights. That’s where code readers and scan tools come in. A code reader identifies the DTC, but a scan tool does more. It may also tell you what the code means and what’s causing it.
“We’ve all been there, feeling stressed, not knowing what’s causing the problem. This is where a code reader helps—it lets you see the specific diagnostic trouble codes that pinpoint exactly what system needs attention,” says tech expert and engineer Robert Johns. “During my time in the industry, I relied on code readers a ton to diagnose issues. When something goes wrong, the computer stores a diagnostic trouble code corresponding to the faulty part. The code reader shows you these codes so you know precisely where to focus your diagnosis. It also erases codes to turn off the check engine light after repairs.”
The well-priced Ancel AD310 Code Reader does everything it should and more. The easy-to-use plug and play unit starts quickly and prompts you through each diagnostic step. It can reset I/M readiness monitors. And its three-year warranty makes this product a winner for the beginning DIYer.
The Autel ‎MaxiLink ML629 Scan Tool comes with lots of nice features. This small scanner can read and clear ECM, PCM (powertrain), SRS (airbag) and the ABS codes, as well as run an I/M self-test to verify whether your vehicle can pass emissions testing. Free lifetime updates, 24/7 tech support and PC and Mac compatibility makes this scanner one to consider.
The VeePeak OBD Check BLE+ Bluetooth code reader is nicely priced and easy to set up right out of the box. It works with your iOS or Android phone. Besides its code reader functions, choose which performance information data (PID) to display on the customizable “dashboard.”
Straightforward and convenient, this scanner checks I/M monitors and oxygen sensor (O2) operation, the same as many professional scan tools. You can purchase additional apps to increase functionality.
Updated for 2022, the ‎Launch CRP129X Scan Tool comes programmed with most of the same functionality as the Launch CRP129E reviewed below, but with a lower price tag.
It takes screenshots in case you need to show your mechanic what you found. Its 6100mAh built-in rechargeable battery, plus a five-year warranty and lifetime free updates, make this a worthwhile investment.
Full of features, the Foxwell OBD2 NT624 Elite Scan Tool can check electrical devices (power seat, lights, HVAC, etc.) as well as engine sensors to diagnose “no-code” drivability issues.
Although lacking TPMS reset, the five service resets it does offer, including throttle adaptation — needed after cleaning the throttle body — are nice touches. The included microSD card lets you print data reports from your PC. All that, plus free lifetime updates, will make this a welcome addition to your automotive tool kit.
The ‎Launch CRP129E Scan Tool ships with all the functionality you’ll probably ever need. Nice features include its ability to reset five service monitors and read PIDs, coupled with the five-inch HD intuitive touch screen and easy-to-navigate interface.
Pro features including live data sampling displaying component status or sensor behavior via voltages and graphs. It generates and prints a vehicle health report card, helpful when planning future maintenance. With free updates, long-life battery and a charging cable, this scanner will quickly pay for itself.
The bi-directional 2024 Model Launch X431 V Pro 4.0 offers the same functionality and innovative features of a pro scanner costing four or five times as much. It can program key fobs, flash (reprogram) the ECM, calibrate the advanced driver assistance systems (ADAS) and more — functions usually only possible with a manufacturer’s scan tool.
With a programmable eight-inch HD touch screen, input buttons and WiFi and Bluetooth support, this scan tool does everything you could ask for.
Code readers offer a place to start when diagnosing a check engine light. Any number of issues can trigger a single DTC, so code readers are less helpful than a scan tool. “Code readers work well for general troubleshooting and simpler fixes since they’re affordable and user-friendly,” says Jones. “But sometimes a full scan tool is better, like if you need live data, module-specific work or repair verification.”
Besides reading/clearing codes, a scan tool can read live sensor data, beneficial when diagnosing a CEL or other car troubles. Using a scan tool as part of your regularly scheduled maintenance ensures your emission system is operating properly, increases fuel economy and even reduces repair and maintenance costs.
Here’s what to look for:
These scan tools and code readers are NOT for use on hybrid or electric vehicles.
Not everyone needs the most comprehensive scan tool available. If you’re just troubleshooting your family’s vehicles to avoid expensive diagnostic fees or keep your vehicles roadworthy, take a look at these scan tools and code readers.
If you enjoy working on your vehicle or just want to avoid expensive diagnostic fees (like paying $50 to $100 to be told you have a loose gas cap), a DTC code reader or scan tool makes an excellent investment.
Code readers and scan tools plug into your vehicle’s 16-pin universal Assembly Line Diagnostic Link (ALDL) connector, interfacing with your vehicle’s OBD-II system. Code readers are typically reasonably priced, easy to use, read/clear DTCs and reset the CEL.
Scan tools cost more than code readers. They provide abundant, valuable information to help you quickly pinpoint problems code readers can’t.
