Ultrasonic Backup Sensor System

One of the inside backup warning lights flashes continuously when driving forward. The owner’s manual indicates something wrong with the ultrasonic backup warning system. After review by a mechanic of each of the four sensors individually in the rear bumper (with car running and in reverse0, each sensor seemed to work fine. The mechanic suggested the bumper sensors were dirty; after cleaning (one) backup sensor still flashes.

It would be nice if I knew what kind of car you are refering to. Maybe then I could do the online searching that you should be doing.

The car is a 2002 Cadillac STS.