WARNING: This page is about a different car, the 1990 Buick Riviera and 1990 Buick Reatta. However, it is still accessible from the selected car via links, so may be relevant.
If an intermittent Code B671 is being set, manipulate related wiring while observing BD70 display. If failure is induced, reading will jump from its normal value to a reading less than 3 percent.