VEHICLE SONAR SYSTEM DIDN'T WARNED DRIVER ABOUT OBSTACLE WHICH RESULTED IN HITTING IT CAUSING DAMAGE TO THE REAR WHILE BACKING UP BUMPER. IT WORKS FINE 90% OF THE TIME BUT IT DIDN'T AT LEAST TWICE WHEN MY WIFE HIT LAMP AND 2ND TIME POLL . I TOOK VEHICLE TO BAKER NISSAN EXPLAINED WHAT HAPPENED BUT THEY DIDN'T FIND ANYTHING WRONG WITH IT. WHEN I ASKED HOW MANY TIMES THEY TESTED IT THE RESPONSE WAS: 1 TIME REPRESENTATIVE TRIED BACKING UP AND 1 TIME MECHANIC.