Ford: Ford f250 superduty

Question
QUESTION: 2003 f250 super duty driving along about 55-60 all the sudden abs light flashing when speedometer dropped speed to 35-40 then back to normal?

ANSWER: Hi Kevin, this particular vehicle is very common for the speed sensor located in the rear differential to go bad. it is one of two sensor the computer uses to determine speed and shift points. it is located right on top of the differential in the center. it will have a 2 wire connector going to it and probably held in place with 1 13mm bolt remove this bolt and work the sensor back and forth while pulling up. replace it. readily available in any after market parts store. it is also a good idea to splice in a new pigtail connector as well but I believe this may be a dealer item only but try after market first. they may have caught up with the times. good luck and keep me posted. Happy New Year.

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QUESTION: The 2000 and earlier models have a standard rear wheel anti-lock brake system, while the 2001 and later models are equipped with four wheel abs and have a speed sensor on each front steering knuckle. Is there any way to troubleshoot which sensor could be faulty without replacing all three? Thanks and Happy New Year to you as well.

Answer
the front speed sensors only input to the abs module, the rear speed sensor inputs to the abs as well as the pcm. you can jack up the rear end and put an ohm meter to the sensor and see if it changes while an assistant spins the wheels but it appears the way you explain it, the sensor is going open when it gets warm