What causes speedometer and odometer to not work on a 1990 Chevy Astro Van?

The speedometer and odometer in a 1990 Chevy Astro Van may not work due to a malfunctioning vehicle speed sensor (VSS), which sends speed data to the dashboard. Additionally, issues such as a broken speedometer cable, faulty instrument cluster, or electrical problems can also cause these gauges to fail. Inspecting these components can help diagnose and resolve the issue.