"Hall" sensors

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Vigilante

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So I have a constantly flashing 4 x 4 light on my dash. This research I have done points to "hall" sensors. I have no idea what these are. I replaced my speed sensor on the rear differential and that has made no change. What sensors are on the transfer case that can be replaced? Without looking, my research online has indicated that there is only a shift motor on the transfer case and no sensors. I have yet to change the speed sensor on the transmission. What and where are the sensors that can be replaced?
 

Bedrck47

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These are the speed sensor that are on the transfer case

see attached print mainly 34-03

Send me a PM with your e-mail address and I will send you some information on how to replace them
 

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Steve Ruddy

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My A4WD light blinks, but the 4X4 L or H does not blink, a few years ago I replaced the speed sensor on the rear transfer case because it would not engage without there being loud noises, replacing it stopped the noises and seemed to work but the A4WD light has always blinked, can anyone help me? 1998 Expedition XLT 4x4 - 4.6 V8
 

Todd Campbell

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Sounds like you need to replace the forward input speed sensor. 1997 to 1999, Borg Warner 4406 TOD (Torque on demand) transfer case. Can shift up to 70% of the drive line torque to the front wheels in A4WD mode. Hall effect sensor on the input shaft and output shaft. 1997 also had the VSS in the transfer case. If the transfer case will go in 4x4H when stopped, steady light, but blinks if you select 4x4 when moving 40 mph or more, one of these sensors is bad. If you select A4WD when stopped and the light is steady, but as soon as you exceed 30 to 40 mph it blinks same thing.
 
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joethefordguy

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https://en.wikipedia.org/wiki/Hall-effect_sensor

A Hall-effect sensor (or simply Hall sensor) is a device to measure the magnitude of a magnetic field. Its output voltage is directly proportional to the magnetic field strength through it. The sensor type is named after the American physicist Edwin Hall.[1]

Hall-effect sensors are used for proximity sensing, positioning, speed detection, and current sensing applications.[2]

Frequently, a Hall sensor is combined with threshold detection, so that it acts as and is called a switch. Commonly seen in industrial applications such as the pictured pneumatic cylinder, they are also used in consumer equipment; for example, some computer printers use them to detect missing paper and open covers. They can also be used in computer keyboards, an application that requires ultra-high reliability. Another use of a Hall sensor is in the creation of MIDI organ pedal-boards, where the movement of a "key" on the pedal-board is translated as an on/off switch by Hall sensors.

Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing, tachometers and anti-lock braking systems. They are used in brushless DC electric motors to detect the position of the permanent magnet. In the pictured wheel with two equally spaced magnets, the voltage from the sensor peaks twice for each revolution. This arrangement is commonly used to regulate the speed of disk drives.
 
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