Note On Intermittents
WARNING: This page is about a different car, the 1989 Cadillac Fleetwood and 1989 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
Manipulate transmission and ECM connector and circuit No. 520 wiring while observing parameter P.1.5. Remove and replace ECM and transmission connectors, and ensure they are latched. If circuits check out okay, substitute a known good sensor unit and retest.