How to use an OBD-II scanner to diagnose engine problems
OBD-II scanner courtesy of traderscity.com
The On-Board Diagnostic II (OBD-II) is a reporting system for engine problems, which is present on all vehicles manufactured after 1996. This system illuminates the Check Engine light when it detects a problem. Newer systems have a digital port which allows you to use a scanner to determine the nature of engine problems. These readouts are displayed as Diagnostic Trouble Codes (DTCs). While any auto repair shop can run an OBD-II scan on your vehicle for a fee, many auto parts stores will lend you a scanner free of charge, allowing you to diagnose the problem yourself. Running a scan is simple, and only requires a scanner, along with a pencil and paper to record DTCs.
The OBD-II connector is located under the steering wheel in most cars, and is rectangular in shape with a 16-hole pinout.
After attaching the scanner, turn on your car, but do not start the engine. The scanner will have a set of instructions for you to follow, and will display one or more DTCs, which you should write down. After scanning, you will want to reset the check engine light. Look in your owner's manual before doing this, because the process varies by vehicle, and methods to clear the Check Engine light on one car can lead to future diagnostic errors on others. For many cars, you can reset by disconnecting the negative battery terminal for one minute, and then reconnecting, but check the manual first, since this method can create problems with the powertrain control module on some vehicles.
Alternately, most scanners will have a “clear codes” option you can use to turn off the Check Engine light. After resetting, run the OBD-II scan again to figure out if the DTC codes are “hard” or “soft.”
Hard codes refer to more permanent problems which require immediate attention, whereas soft codes refer to more transient problems. Auto parts stores have code books available to look up these codes, but you can also find lists of DTC meanings online.
Keep in mind that the DTC displayed refers to the system where the problem occurred, and will not actually reveal a specific part to be replaced. For example, a bad spark plug can lead to a misfire code being displayed, but the problem could also be with the head gaskets or fuel injector.
Other DTCs may be soft codes referring to emissions problems which may not impact how your car runs, but could cause you to fail an emissions test. By looking online, you can check for a step-by-step diagnostic guide to find the exact nature of the problem, and determine if this process is something you are capable of doing depending on how comfortable you are with DIY car repair.
—Seth Berger
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