# Spy Networks Tab: J1850 VPW Mode

The [Tools](https://docs.intrepidcs.com/vspy-3-documentation/3.9.12/vehicle-spy-main-menus/main-menu-tools) -> [Options](https://docs.intrepidcs.com/vspy-3-documentation/3.9.12/vehicle-spy-main-menus/main-menu-tools/tools-options), [Spy Networks](https://docs.intrepidcs.com/vspy-3-documentation/3.9.12/vehicle-spy-main-menus/main-menu-tools/tools-options/options-spy-networks-tab) tab lets you select how the J1850 VPW headers are handled as shown in Figure 1.

Option 1: Select the default GM Class 2 version with a three byte header (PT, Trgt, Src).

Option 2: Select Chrysler version with a one byte header (ID).

The J1850 VPW Mode setting affects many areas of Vehicle Spy, including [Messages](https://docs.intrepidcs.com/vspy-3-documentation/3.9.12/vehicle-spy-main-menus/main-menu-spy-networks/messages-view/messages-view-column-headers) view and the [Messages Editor](https://docs.intrepidcs.com/vspy-3-documentation/3.9.12/vehicle-spy-main-menus/main-menu-spy-networks/message-editor/messages-editor-message-fields). When decoding signals, for example, a reference to the first data byte (B1) of a J1850 message actually means a reference to byte 2 in Chrysler mode or to byte 4 in Class 2 mode.

![Figure 1: Selecting the J1850 VPW Mode.](https://2280262322-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FC3KyOmcYmM6ZVd3OQDa1%2Fuploads%2FTyJehjBiNj1hJakgjZA6%2FspyVPWMode.gif?alt=media\&token=ac3f42f8-183f-460e-bc3b-4bd15c65797e)