Question: When I put my 2006 four-wheel-drive F-250 Super Duty in reverse, the backup sensor light stays on and I can't turn it off by pushing the button. The backup warning (beeper) worked fine until a few weeks ago, but now it doesn't work at all.
Answer: The parking aid reverse sensing system is enabled by default when the ignition is cycled off and on. Normally, the light on the switch will turn on for 3 seconds, then go off. Pressing the button will turn the light back on, disabling the system. If the system is enabled, and the light remains on with the gear selector in reverse, there's a fault that will also disable the system. The correct scan tool should provide diagnostic trouble codes to point us in the right direction, but there is a quick test you can perform yourself. Turn the ignition switch on (engine not running), and put the gear selector in reverse (parking brake applied). Go to the rear bumper, and carefully listen to each of the four ultrasonic sensors. Have your ear directly up against each sensor, or use a screwdriver as a stethoscope. You should hear a continuous clicking sound from each sensor. If one of the four sensors is silent, the problem is most likely that particular sensor. I repeat: most likely. There may be an open circuit from the sensor to the module, a bad module, and so on. But the sensor is a common failure, and if one sensor goes out, the entire system will not work.
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