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If you purchased a car after 1996, chances are it has an OBD-II (On-board diagnostics II) port. Every car or truck on the road manufactured after 1996 is legally mandated to have one installed.
OBD-II is an on-board computer that monitors emissions, mileage, speed, and other data about your car. It’s connected to the Check Engine light, which illuminates when the computer detects a problem.
The OBD-II on-board computer features a 16-pin port located under the driver’s side dash. It allows a mechanic or anyone else to read the error code using a special scan tool.
Before OBD-I, each manufacturer had their own set of standards for OBD, meaning that mechanics had to buy expensive scan tools for each manufacturer. OBD-I was first introduced in 1987, and started the standardization of onboard diagnostics.
It had sensors that detected emissions and was able to minimize them through emissions-controlling valves. However, it had many problems and shortfalls.
As a result, in 1996 car manufacturers started to equip cars and trucks with an OBD-II port. Every system is mostly the same, but there are slight variations. These are known as protocols, and are specific to vehicle manufacturers.
There are five basic signal protocols:
Pins 4 and 5 in all protocols are used for ground connections, and pin 16 is used for power from the car’s battery.
Once the computer senses a problem with the engine or any other component of the car it’s monitoring, it’ll trigger the Check Engine light. Some vehicles also blink the engine light if the problem is a very serious one.
Diagnostic Trouble Codes (DTC) are stored in the computer system. Codes can vary from one manufacturer to another. However, anyone with an OBD-II scan tool can connect to the port and read the diagnostic trouble codes from the computer.
The reason any OBD-II scan tool can read the codes is because of the standardized pinout. Scan tools can read from any of the protocols listed above. The standardized pinout is as follows.
OBD-II scanners can connect to these ports and identify the trouble code from any manufacturer that uses one of the OBD-II protocols.
Traditionally, a mechanic would hook up a scan tool to the port to read the DTC. Less expensive scanners would only provide a numeric code, which the mechanic would then look up from the manufacturer’s manual or service website. More expensive scanners provide will provide text error codes.
However, in recent years, there are more advanced tools available for regular drivers who don’t want to have to depend on a mechanic to find out what’s wrong with their car.
One example is the OBDLink SX USB Adapter by ScanTool that lets you read the trouble codes with your laptop.