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If the braking system shows no signs of an issue you could have a faulty ABS module or a wheel speed sensor fault to trip the system as it is seeing a wheel not moving properly and will deactivate the system. Make sure that the brake fluid level is good, if low you will need to find where the leak is from, this vehicle did have a recall for the brake pressure switch for a leak which could be causing a module issue if found to be leaking. It is somewhat common to see an module fault with an internal relay issue or a valve fault which will require a new module to address. There are quite a few possibilities to what the fault could be (module, speed sensor, wiring issue, etc...). To prevent from throwing a bunch of un-needed parts at it, it would be best to have the system scanned for codes to pinpoint where to start for diagnosis.
Most auto stores check for codes for free, some shops cannot check for an ABS code and may require having a shop do this. You may call around to some auto stores to see if they can scan 'ABS' codes and if not call some independent shops to see if they will do this for for free or a small charge. With this code I can assist in where to go next. I can help without a code but will take a lot of testing to find the fault.
Brake fluid is full; the switch under recall has been replaced under the Ford recall campaign. This issue comes and goes. Have had the vehicle for 5.5 yrs and can't seem to find a solution
If a wheel speed sensor is at fault the light will be on just about anytime you drive the vehicle. One thing may note is if this happens at a certain speed this can be a wheel speed fault which loses a signal at that time to set the code. If the light comes on for no reason the module is most likely the fault as the internal relay is most likely bad. The module relay issue is the most commonly seen thing to cause an intermittant light issue.