- Remove the front bumper by backing out 10 or so small screws along the underside of the bumper. It should pop off easily. Be careful not to damage the wire harness. Disconnecting the harness is not necessary.
- Using canned air, blow out the dust from the entire inside of the bumper. Pay special attention to the IR sensors (they're the small LEDs).
- Reassemble and test.
This appears to be a common problem with a simple solution. HTH