Beginning in 1996 the U.S. government required a second generation diagnostic system, also know as On Board Diagnostic II (OBDII) on all vehicles sold in the United States. This Diagnostic Trouble Code (DTC) information is accessible to technicians without using the manufacturers scan tool. The manufacturers VAG 1551 VW scan can be used in generic mode to retrieve the trouble codes. While the VAG 1551 is not the only code retrieval device that can be used it is the only one discussed in this guide. For information on other models, check with you local aftermarket parts supplier.