Best Cheap OBD-II Scanners and What They Can Do

Every gasoline car and light truck sold in the US since the 1996 model year has an OBD-II port, and a basic scanner that reads it costs less than one diagnostic fee at a shop. The catch is that "OBD-II scanner" covers everything from a $20 code reader to a tool that can command your ABS pump. This guide sorts the categories by what they can actually do, so you buy the cheapest one that covers your car and your skills.

We do not rank brands here. Models change every year and the same hardware is often sold under many names. Instead, use the feature checklist below to judge any scanner you are considering.

The generic OBD-II standard guarantees a minimum set of functions on every compliant vehicle. Any working scanner, even the cheapest, should handle these:

• Read stored and pending powertrain codes. These are the P0xxx codes behind the check engine light, such as P0420 or P0171. Pending codes are faults seen once that have not yet turned the light on.
• Clear codes and turn off the check engine light. Useful after a repair, but read the warning about readiness monitors below before you do it.
• Show readiness monitor status. These tell you whether the car's self-tests (catalyst, EVAP, oxygen sensors and others) have run since the last reset. Emissions inspections check them.
• Show freeze frame data. A snapshot of engine speed, load, coolant temperature, fuel trims and vehicle speed at the moment the code set. This is often the most useful diagnostic clue a cheap tool gives you.
• Read the VIN on most 2000s-and-newer vehicles. You can paste it into our VIN decoder to confirm the exact year, engine and trim before ordering parts.

If a listing advertises these as premium features, it is selling the minimum.

Prices are typical estimates and vary by retailer and season. Professional bidirectional tools that cost well over $500 exist, but most owners never need one.

Basic code readers

A wired reader plugs in, powers itself from the port and shows the code on a small screen. There is no app, no account and no battery to charge. The limitation is that most cannot show live data, or show it so slowly that it is not useful for diagnosis. For "why is my light on, and is it safe to drive to the shop," that is enough.

Bluetooth and Wi-Fi dongles

A dongle is a small adapter that stays in the port and talks to an app. The hardware matters less than the app: the same adapter can be nearly useless or very capable depending on the software. Many cheap dongles are clones of the ELM327 chip. Some work well with generic apps; others drop connections or do not support every protocol.

Things to check before buying:

• Whether the app is free, a one-time purchase, or a subscription to see codes you could read for free elsewhere.
• Whether it supports iPhone, Android or both. Some adapters use connection types that one platform does not support.
• Whether "ABS and airbag" support is included for your make, or sold per manufacturer as an add-on.

Handheld scan tools

These add the systems beyond the engine: ABS, airbags (SRS), transmission and body modules. Many also do service functions such as oil-life reset, electronic parking brake retraction for rear brake jobs, steering angle sensor calibration and battery registration. If you plan to do your own rear brakes on a car with an electronic parking brake, check that the tool supports that function for your exact make and model year.

Not every feature on the box helps an owner. These are the ones that change what you can diagnose at home.

Live data with graphing

Being able to watch sensor values while the engine runs turns a code into a diagnosis. Three readings do most of the work:

• Short-term and long-term fuel trims. These show how hard the computer is correcting the air-fuel mixture. They are the core of diagnosing lean codes like P0171 and P0174.
• Upstream and downstream oxygen sensor voltage. Comparing the two is how you judge a catalytic converter before replacing it for P0420.
• Coolant temperature. A thermostat stuck open often shows as an engine that never reaches normal temperature, which also sets P0128.

A graph is far more useful than a number that updates once a second, because many faults are patterns.

Mode 06 test results

Mode 06 shows the raw results of the car's onboard self-tests, including misfire counts per cylinder on many vehicles. It can point to a weak cylinder before a misfire code like P0300 ever sets. The data is cryptic on some apps, so look for one that labels the tests in plain language.

Manufacturer-specific codes

Generic codes start with P0. Manufacturer codes, such as many P1xxx codes and most body, chassis and network codes (B, C, U), often need a tool with make-specific software. If your car has an ABS light, a basic reader will show nothing at all.

Bidirectional controls

This means the tool can command a component: cycle the ABS pump to bleed brakes, run the EVAP purge valve, turn a cooling fan on. It is helpful but not essential for most owners. Be skeptical of cheap tools that claim full bidirectional control across every brand.

• "Repair solutions" and "verified fixes." Some tools show a list of the most common fix for a code. It can be a fair starting point, but it is not a diagnosis. Replacing the "most common" part without testing is how people buy three oxygen sensors for one vacuum leak.
• Battery and alternator tests through the port. The tool can read system voltage, which you can also check with a $15 multimeter. It cannot load-test a battery.
• Huge code libraries. Every tool can look codes up. You can also look up any code free on our OBD-II code pages, which list meaning, common causes and fixes.

1. 1Confirm your car is OBD-II. US gasoline cars and light trucks from model year 1996 on are covered. Light-duty diesels were phased in starting with the 1997 model year. Find the port under the dash on the driver's side, usually within reach of the steering column. Your owner's manual shows the exact spot.
2. 2Decide which systems you need. Engine only? Any cheap tool works. ABS, airbags or service resets? You need a tool that lists your make and year for those functions.
3. 3Check the app's real cost. Read what is free and what is a subscription before you buy the hardware.
4. 4Look for live data graphing and freeze frame. These matter more than screen size.
5. 5Check update policy. Handhelds with make-specific features often limit free software updates to a period of time.

1. 1With the engine off, plug the scanner into the port. Turn the key to on (or press the start button without your foot on the brake) and let it connect.
2. 2Write down every code and its freeze frame before you clear anything. Take a photo of the screen. Once cleared, that data is gone.
3. 3Look each code up, starting with the first one that set. One fault can cause others. A misfire, for example, can trigger a catalyst code later.
4. 4Check readiness monitors. If several are "not ready," the codes may have been cleared recently, which is worth knowing when you are buying a used car.
5. 5Fix or diagnose, then clear the codes and drive normally for a few days. If the code returns, the repair did not address the cause.

A code tells you which test failed, not which part is bad. P0420 means the computer judged catalyst efficiency too low. The cause might be the converter, but it can also be an exhaust leak, a lazy downstream sensor or an engine that has been misfiring. The scanner is the start of a diagnosis, not the end.

A scanner also cannot see mechanical faults that the computer does not monitor: worn suspension, brake pad thickness, a leaking water pump. A code-free scan is not a clean bill of health on a used car.

Keep a record of what you found and what you replaced. Logging each code and repair in your free CarManager garage makes repeat problems obvious and helps when you sell.