P0700 in a 1996 Chevy Astro van means there's a
problem with the transmission control system. It's a generic trouble code, meaning it doesn't pinpoint the exact issue. The code indicates the PCM (Powertrain Control Module) has detected a malfunction within the transmission's electronic controls. This could be anything from a faulty sensor or solenoid to a wiring problem or even a failing transmission control module itself.
You'll need further diagnostics to determine the root cause. A mechanic can use a scan tool to access more specific codes and data from the transmission control system to pinpoint the exact problem. Ignoring P0700 could lead to more serious transmission damage.
