Many performance problems can be identified on a VW Passat by connecting the vehicle to a computer using a special cable. The codes read from the vehicle's internal computer can provide insight into many vehicle issues, and speed the repair process.
Choose either a VCDS cable or a standard OBD-II scanner. OBD-II scanners, which are readily available from auto parts stores, will read codes, though the results will not be as detailed as using the VCDS system. If you choose OBD-II, skip to Step 4.
Determine the appropriate VCDS cable. If the model year is between 1995 and 2005, you will need either a HEX-USB+CAN, HEX-COM+CAN, KII-USB or KEY-COM cable. After 2005, only HEX-USB+CAN, HEX-COM+CAN and Micro-CAN will work.
Purchase a VCDS cable from Ross Tech, a company that specializes in scanning software for VWs (see Resources). You will also need a computer: a laptop is recommended.
Find the car's interface port. In newer vehicles, this is located on the left side of the driver's side footwell. In older models, typically before 2005, it is usually located in the center console by the cigarette lighter. It will be labeled in most cases.
Turn your vehicle's ignition to the "accessory" setting and follow the instructions for your specific reader. When the scan is complete, note the codes that the reader will display.
Perform any maintenance needed to remedy the problem. If you do not have the needed skills or experience, take the car to a mechanic. After the work is complete, test drive the car and rescan to ensure that the issue has been fixed.
