What do you do when a warning light comes on? If it's the Check Engine light most of us keep driving. If it's signaling an anti-lock braking system (ABS) or supplementary restraint system (SRS - airbag) fault we might be more concerned.
The only way of knowing if the problem is serious is by reading and interpreting the Diagnostic Trouble Code (DTC). DTC's are retrieved by plugging a code reader or scanner into the On-Board Diagnostic (OBD) port. A repair shop can do this for you, but if you own a code reader or scanner you can do it yourself.
Once you know what the problem is, if it's a quick fix or you have some mechanical skills you might do the work yourself. Alternatively, if you take the vehicle to a shop you'll know if they are giving you good advice about the problem.
There are many different types of scanners and code readers and features and prices vary widely. This buying guide will help you find the best car code reader for your needs. It covers:
- A (brief) history of On-Board Diagnostics
- The difference between scanners and readers
- Why buy a scanner or reader
- Vehicle make and model compatibility
- Features to look for
Once you're familiar with these products we'll review eight of the best obd2 scanners and readers.
A (brief) History of On-Board Diagnostics
OBD systems were first developed for checking vehicle emission control systems. They consist of sensors that send data to the Powertrain Control Module (PCM). This compares the actual values with the limits for that vehicle. If they are exceeded the warning light comes on.
In the 1990's OBD2, (sometimes written as OBDII) came out. This provided far more information about the vehicle systems. Since 1996 all cars and light trucks sold in the US have come with an OBD2 port. More recently vehicle makers have added status checking and reporting of the ABS and SRS systems.
The OBD2 port is usually found under the steering wheel. It looks like an old-style computer monitor terminal.
The Difference Between Scanners and Readers
You may see and hear the terms “scanner” and “reader” used interchangeably, but they are not the same. Both plug into the OBD2 port, let you reset the warning and turn off the Malfunction Indicator Light, (MIL). However, the code reader only displays the DTC. It won't explain what it means or provide any diagnostic help. For that you'll need to go online. (Some readers come with a list of codes, but these may not cover your specific vehicle.)
A scanner differs in two ways. First, it can pull live data from the PCM, and often also the ABS and SRS systems. Second, it provides help with diagnosing the problem. The more expensive readers can also do some of these things so there's no clear line between the two.
Why Buy a Scanner or Reader
The main reason is to find out why a warning light has come on, and to turn it off. You might also use it to monitor or improve the performance of your car. You could also use it to diagnose an intermittent fault. They make good gifts for car enthusiasts, in which case you'd want to buy the best car OBDII scanner you could afford!
Vehicle Make and Model Compatibility
Vehicle manufacturers use several different protocols for their OBD2 systems. Most scanners and code readers will work with vehicles from the major car companies but it's a good idea to check before buying.
Features to Look For
Every OBD2 scanner and reader shows and allows you to reset DTC's. They will also let you turn off the MIL. After that there are a lot of other features to consider. Here's a list:
Problem-solving capabilities and support
Reading a DTC is only the first step in solving the problem. You need to find out what the code means, and how to fix it. Almost all scanners and readers offer a table that explains the code although you can just go online. The better scanners provide a lot of support for diagnosing problems and identifying solutions. Some information comes on CD, other material you access online.
ABS and SRS code reading
Entry-level readers will only output engine DTC codes. If you want to diagnose warning messages from the braking or airbag systems, look for the ability to read these codes.
Most scanners and readers are hand-held units with a cable that plugs in to the OBD port. Some use a Bluetooth transmitter plugged into the port which sends data wirelessly to an app on your phone or laptop. One advantage of this is that you can quickly access online databases of problem-solving tips from your device.
If using a plug-in scan tool, check the cable length. A short cable is okay if you're just going to read a code in your garage but one that's longer lets you put the scanner on the passenger seat. You might even want to carry it around to the front of the vehicle while you're working under the hood.
Storing data helps understand problems. You can see when a particular code last occurred, save data for subsequent analysis and see what effect any changes you make have. You might also want to have the scanner plugged in while driving. If that's the case you definitely need some memory to save your data.
This means the scanner retrieves information showing what the vehicle was doing when the fault occurred. It's helpful for finding out what triggered a DTC.
Hooking your scanner to a PC offers two benefits. You can download updates covering newer vehicles and you can save and print data. (This would be helpful if you wanted to monitor trends.)
Size and weight
Basic readers have a simple LCD display. A larger screen with a color display lets the device show more information. The best ODB2 scanners even display data graphically.
The downside of a larger screen is that the unit becomes bigger and heavier.
If you have short stubby fingers or prefer working in latex gloves you'll be glad of big buttons.
Less expensive readers and scanners are powered through the ODB port. This means data is not available once you disconnect. It also risks draining the vehicle's battery if you leave the unit plugged-in for an extended period. Units that run on batteries avoid this problem.
Scanners with larger screens can display selected live data, (usually termed Parameter ID's or PID's) in a graphical form to help with analysis.
I/M Readiness and Smog Check
Smog check lets you see if your vehicle will pass emissions testing. The I/M function, which stands for “Inspection & Maintenance,” is a check of how much time has passed since any DTC's were reset. (Without this people might be tempted to cheat on their emissions tests.)
A scanner with this function can display the upper and lower limits of each parameter, and so see exactly why a DTC was signaled. It's a function that's of most use to those with expert engine knowledge.