Note on Intermittents
WARNING: This page is about a different car, the 1990 Cadillac Fleetwood and 1990 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
Manipulate VSS wiring and connectors and verify wiring is not close to spark plug wires. Code can be caused by an open, short to ground or short to voltage on circuit No. 400 or 401. Also, check for an open or shorted sensor connector, engine-to-dash connector, ECM connector or a defective sensor. If wiring and connectors check out okay, substitute a known good sensor and retest.