One problem related to brake sensor has been reported for the 1999 Buick Lesabre. The most recently reported issues are listed below.
Brakes are spongy; partially due to a racing engine, it takes more pressure to apply the brakes for what would be considered a routine stop. The engine has 'automatic cruise control' which distorts normal driving sensors. I drove a similar Buick for a day and it didn't require me to brake frequently to avoid exceeding our condo area's speed limit.