Since 1996, all cars and light-duty trucks manufactured in the United States are required to have a standardized on-board diagnostic system, also called an OBD-II system. The OBD-II is currently in its second generation, as the name suggests.
The first generation of on-board diagnostics were not standardized. In those days, each automotive manufacturer had their own unique method for diagnosing mechanical problems. Chevrolet, for example, used a sequence of check engine light flashes to signify specific problems.
The OBD-II standardized system was originally designed to test and monitor vehicle emissions. The system was outfitted with a standard pin connector within 2 feet of the vehicle’s steering column for easier access. Manufacturers are only required to send emission-related data to the port. However, most have elected to use this port to access and check the entire electrical system.
What are Engine Codes
Most of the components within a vehicle’s engine and transmission system (known as the powertrain) are monitored by a centralized computer system. The computer constantly checks the inputs and outputs of the powertrain components and makes minor adjustments as necessary to keep the system running smoothly.
There are other systems within the vehicle that are also monitored. These systems include, the airbags, brakes, fuel, crash detection systems, and all the other electrical components of the vehicle.
Occasionally, a component within the vehicle will misfire, malfunction or fail. When this happens, the computer logs the error and turns on a dashboard indicator light, usually the check engine light.
System errors are logged as five character codes. The first character signifies which part of the vehicle’s system experienced an error. The last four characters represent the actual error. Powertrain error codes begin with the letter ‘P’. Chassis related codes begin with a ‘C’. ‘B’ codes are related to the body, and the letter ‘U’ signifies an error in the Network.
The primary check engine codes that the OBD-II system uses are standardized based on the Society of Automotive Engineers (SAE) protocol. Each manufacturer is allowed to create additional codes to assist with troubleshooting problems within their vehicle’s specific systems.
Explanation of Code Readers vs. Scan Tools
Because the data port and error encoding are standardized, there are many tools on the market that allow backyard mechanics and automotive professionals alike to access the system.
The tools that access the OBD-II system fall into two categories:
- Code Readers
- Scan Tools
OBD-II code readers are the simpler of the two tools. They are used to see any error code(s) and they also allow the user to delete the error code log. By seeing the codes, the user can begin the process of repairing the vehicle. Deleting the codes should turn the dashboard indicator light off.
The better, and often more expensive, code readers show the meaning of the error codes. With the cheaper models a CD or code book is provided to look up the meaning of the error code.
OBD-II scan tools are more expensive than code readers but they provide more access to the on-board diagnostic system.
The level of access and the information displayed varies depending on the scan tool model purchased. Base model scan tools are only programmed for a couple of the basic modes of operation. They typically display powertrain-related codes, the meaning of those error codes, and emissions data. The OBD-II protocol allows as many as 10 modes of access to the diagnostic system.
The best OBD-II scanners operate in more modes and can display live system data, error codes, and even access vehicle-specific information such as the VIN, software ID, and verification information.
Comparison Table
| Scanner | On-Screen Definitions | Rating | Price | Notes |
|---|---|---|---|---|
| Actron CP9125 | No | 4.5 | $$ | Most basic level Actron code reader |
| Actron CP9550 | Yes | 4.5 | $$ | Compatible with all 1996 and newer |
| Actron CP9575 | Yes | 4.4 | $$$ | Internet updateable. No ABS |
| Actron CP9580A | Yes | 4.4 | $$$$ | Internet updateable. ABS for Ford, GM, Chrysler |
| Autel MaxiScan MS300 | No | 4.4 | $ | |
| Autel AL301 | No | 4.2 | $$ | Newer version of MS300 |
| Autel MaxiScan MS309 | Yes | 4.1 | $ | |
| Autel MaxiScan MS310 | Yes | 4.3 | $$ | All 1996 and newer. Display complete live engine data stream |
| INNOVA 3020 | No | 4.3 | $$ | Must connect to computer for additional information. Reads and erases ABS codes. |
| INNOVA 3030 | No | 4.2 | $$ | Must connect to computer for additional information. Reads and erases ABS codes. |
| INNOVA 3100 | Yes | 4.3 | $$$ | |
| INNOVA 3120 | Yes | 3.9 | $$$ | 3 star reviews typically call it overpriced |
| INNOVA 3160 | Yes | 4.2 | $$$$ | |
| XTOOL PS100 | Yes | 3.3 | $$ | New to the market. |
| XTOOL U480 | No | 4.1 | $ | Very basic code reader. |
| XTOOL U485 | Yes | $$ | Brand new. Only one rating so far. | |
| XTOOL U581 | Yes | 2.8 | $$ | New to the market. |
The Ten Modes of Operation
| Mode | Description |
|---|---|
| 01 | Shows current data available to the scan tool- Powertrain only |
| 02 | Shows freeze frame data. |
| 03 | Shows confirmed diagnostic trouble codes stored in the system |
| 04 | Allows codes from Mode 3 to be cleared |
| 05 | Displays test results from the O2 sensor (non CAN only) |
| 06 | Displays test results for other components within the system (CAN only) |
| 07 | Shows diagnostic trouble codes detected during the last or current driving cycle |
| 08 | Allows the test device to control the operation of on-board components and systems |
| 09 | Requests vehicle-specific information, including VIN, software ID, and calibration verification numbers |
| 0A | Shows permanent diagnostic trouble codes that have been stored as a permanent error code |
What is CAN?
It’s common to see references to ‘CAN’ when researching OBD-II diagnostic tools. So what is it?
The controller area network (or CAN) is one of the protocols used to define the OBD-II system. The CAN is the system that connects all the electrical components within the vehicle to a central control unit.
The main systems connected through the CAN are the Engine Control Unit (ECU), Transmission Control Unit (TCU), Anti-lock Braking System (ABS), and the Body Control Modules.
The ECU controls timings and inputs of engine systems, monitors the outputs, and makes necessary adjustments for system optimization. The ECU also shares data, like engine speed, with the transmission control unit. Data sharing between these systems controls mechanical operations like gear shifting in automatic transmission vehicles. The ECU and TCU are grouped together in modern vehicles and simply referred to as the Powertrain Control Module (PCM).
Data from the CAN can be accessed with scan tools that have Mode 6 capability. These scan tools are able to access and display test results and data provided by system components.
Autel MaxiScan MS310
The Autel MaxiSan MS310 is a helpful device for novice users that occasionally need to diagnose a check engine light. The MS310 is compatible with all OBD-II vehicles, manufactured since 1996.
The MS310 operates in Modes 01-04 & 07. It displays freeze frame data, error codes, live-stream data and allows the user to delete stored codes. With just two buttons, the interface is intuitive and easy to navigate.
However, there are two common complaints with this unit. Some users find this device to be cheaply made. Also, the CD that it comes with is not yet compatible with Windows 7 or 8, although this does not impact the device itself because the error codes and their definitions are displayed on the device’s screen. Nevertheless, the ‘cheaply made’ complaint has some merit, which is why this device is better for light use.
Overall, the Autel MaxiScan MS310 unit is best-suited for backyard use. You can read and clear your codes, and watch the live data stream if that sparks your interest. At less than $20, many automotive-enthusiasts find the MS310 to offer the right amount of functionality at an affordable price. A more detailed review of this scanner is available here.
Actron CP9575 Auto Scanner
The Actron CP9575 is considered a mid-level scan tool. This model reads codes, provides definitions, deletes error codes, displays live engine data and works in Mode 9 to retrieve vehicle-specific information. You can also easily update this device online.
The 4-button interface provides efficient navigation once you get used to the system. Some users find the large words ‘Read’ & ‘Erase’ printed on the up and down keys to be confusing. However, these are simply shortcuts for code reading if you press and hold them down. If you press the buttons normally, they will simply scroll up and down the menus.
Overall, the Actron CP9575 provides a lot of data about your vehicle in a very compact interface. For a combination of basic trouble shooting and detailed system stats, many users find this scan tool well worth the $97 price tag. We covered this model with a more detailed review.
Actron CP9580A Enhanced Auto Scanner Plus
On the upper end of hand held scan tools is the CP9580A by Actron. This tool provides all of the functionality of the CP9575, with added functions like system data graphing and the ability to read and erase ABS codes for GM, Ford & Chrysler vehicles.
Many users find the data graphing very useful for advanced troubleshooting of the powertrain system. You can plug this device into the vehicle’s computer system before a drive, and the device collects multiple freeze frame points during the commute. The scan tool displays the collected data for each system on an easy-to-view graph.
Many users find the interfaces of this tool to be very intuitive and easy to navigate right out of the box. However, some users find the ABS diagnostics very limiting since only GM, Ford & Chrysler codes can be accessed, read and deleted.
Nevertheless, for a high-end scan tool the CP9580A offers a full range of functionality and versatility. It is also very user-friendly. A more in-depth review is also available.
Choosing a Scan Tool
Choosing the best OBD-II scanner comes down to two basic factors, budget and desired functionality. The three tools detailed above provide the greatest range of features at their respective price points. But there are multiple options available for every price range.
Code readers are ideal for casual DIY types that are looking for a simple analysis of the check engine light. Whether or not the code reader provides on-screen definitions of the code isn’t too important. There are multiple websites that provide trouble code definitions.
Serious mechanics and gear heads should choose a scan tool that provides live data streaming so systems can be read while the engine is idling and during test drives. The more data the device collects and displays, the easier it is to fine tune the powertrain system for the maximum performance every car enthusiast desires.