ABS system

[dr pepper]

99 explorer, I recently changed my speed sensor located in the rear diff.. It send s info for the tranny and abs . Now when you just about come to a complete stop the abs engages. The abs is functioning but at the wrong time. Any info would be great.

 

[drdoom]

Does it do that if you put the old sensor back in?

 

[Joushou]

The ABS works by reducing and/or completely removing hydraulic brake pressure when speed data from all sensors do *not* match. In other words, when a wheel slips, and resetting when the speed data matches.

If the ABS isn't working, you should see/hear/feel your wheels slipping. If it "works" at lower speeds, then I think you're just not pressing the pedal hard enough, or there's a fault causing you not to be able to deliver the required brake pressure in order to block a wheel. The ABS on the Explorer feels a bit different than other ABS systems, in my opinion. It doesn't kick your foot, it's more like a weak hum.

(I think we only have 3 sensors on the explorer, 2 for front, one shared on back, meaning there's a possibility that a tiny slip on the rear axel could occur before the ABS engages... It depends on the sensitivity on the system.)

To sum things up, the ABS isn't faulty if you can't block the wheels, as there's nothing there for it to do.

 

[my98nnj]

. Now when you just about come to a complete stop the abs engages. The abs is functioning but at the wrong time. Any info would be great.

This is sort of a common issue here. You probably have another sensor, most likely a front, starting to get weak. Try taking them out and cleaning up the sensor, they tend to get full of gunk and have a hard time reading the tone ring correctly.

 

[dr pepper]

Thanks everyone for your input, but I have solved this mystery gang. The plastic retainers have become brittle and broke off the wiring plug (NO WAY!). This caused it not to be completely seated. I used bailing wire to hold it in position and tested my theory. And the winner is ; An improperly seated connector causes this problem.

 

[Joushou]

Glad you got your issue fixed.
From an engineers point of view, that's not just odd, but dangerous... The ABS system should disable permanently when a fault has occurred, and seeing it's not locking off your brake pressure at all times, it should've realized that the sensor wasn't reporting back. (No signal = wheel block -> reduce brake pressure until it unlocks.)
By not disabling, even though a fault is recognized, puts you at risk, seeing it's speed data is no longer correct, and it cannot correctly administer brake pressure reduction, and risks reducing the brake pressure unnecessarily, and most likely at a time where you need it.

But hey, if my ABS starts acting up, now I know what to look for!