How to Reprogram a PCM

The PCM (powertrain control module) is your car's on-board computer. It controls a myriad of the car's features, including emissions specifications, idle speed and brake control. The PCM can be reprogrammed to improve the car's performance or to fix a bug that negatively affects one or more of the car's characteristics (the car maker creates updates to the PCM software periodically), which is usually done at a dealership. You can update your car's PCM yourself, however, with the right scan tool and the updated PCM software.

Obtain the PCM software specific to your make and model -- you can download this software online from the vehicle maker's website, or you can order a CD with the software on it. Both of these options usually involve paying a fee, although this can vary with different auto companies. When getting your PCM software, make sure that it is specific to your exact make and year.

Connect the scan tool to your computer and start the PCM software program to transfer the information to the scan tool; some auto companies require you to validate your car's VIN and other information throughout this process. After the transfer is complete, disconnect the scan tool and locate your car's PCM -- as this location can vary based on your vehicle, check the owner's manual for the exact location (it is usually located around the car battery). After locating the PCM, find the OBD II connector on the PCM (refer to owner's manual here also).

Turn your car's ignition on, connect your scan tool to the OBD II connector on the PCM and then turn the scan tool to its "On" position. Depending on the make of your car, you will have to select several specifications regarding your vehicle (engine and fuel system details). After providing this information via the scan tool, start the data transfer. Make sure to keep the scan tool connected to the PCM throughout this entire process; the scan tool will alert you when the transfer is completed.

Turn the scan tool to its "Off" position after it alerts you that it has finished reprogramming your PCM. Disconnect the scan tool from the OBD II connector and then turn your car's ignition off. Restart the car to make sure that the codes have been installed properly and that there are no warning lights on your display.