> For the complete documentation index, see [llms.txt](https://docs.intrepidcs.com/vspy-3-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.intrepidcs.com/vspy-3-documentation/3.9.15/vehicle-spy-main-menus/main-menu-tools/tools-options/options-spy-networks-tab/spy-networks-tab-j1850-vpw-mode.md).

# Spy Networks Tab: J1850 VPW Mode

The [Tools](/vspy-3-documentation/3.9.15/vehicle-spy-main-menus/main-menu-tools.md) -> [Options](/vspy-3-documentation/3.9.15/vehicle-spy-main-menus/main-menu-tools/tools-options.md), [Spy Networks](/vspy-3-documentation/3.9.15/vehicle-spy-main-menus/main-menu-tools/tools-options/options-spy-networks-tab.md) 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](/vspy-3-documentation/3.9.15/vehicle-spy-main-menus/main-menu-spy-networks/messages-view/messages-view-column-headers.md) view and the [Messages Editor](/vspy-3-documentation/3.9.15/vehicle-spy-main-menus/main-menu-spy-networks/message-editor/messages-editor-message-fields.md). 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://2396693198-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FlRJv2XDCMeZSU0VbeZlG%2Fuploads%2Fgit-blob-9b330ff98a2bac948d2ece2cdf0dd74c846a5eab%2FspyVPWMode.gif?alt=media)


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