2000 Sable ABS issue

[dalem01]

Good evening,

Old member, been gone for long time, just registered again.

Sorry if discussed before but it's late and past my bed time. A quick search for ABS brought me nothing, not sure why.

We have a new (used) 2000 Sable wagon. It has an unusual ABS issue, which throws no code.

When speed get somewhere below 20mph, the ABS pump kicks on and lightly pulsates on the brake pedal. This happens most of the time and only under 15-20mph.

Using a bluetooth OBDII scanner and FORscan, I tapped into the abs PIDs. I thought maybe a bad/weak wheel speed sensor, but all 4 run nearly identical. Certainly nothing way out of range as I was expecting, like one coming to a rest compared to others. Maybe 2 MPH variances with no one seeming any different from others.

What I do see is both RL and RR inlet (repressurization?) solenoids coming on. I have not located or seen the ABS pump/valve system, but one system I was reading on has individual ports that go to each of the front wheels where the rear use a single/common port that takes care of both rear wheels. My scanner shows one for each rear wheel, so,,,,,,???

Does anything here ring a bell with someone here? I'm sure Ford likely has the same system, but don't know about posting same question over there.

Thanks in advance for any suggestions to come my way.

Dale

[shorod]

Does your Sable have a button in the instrument cluster for "Traction control On/Off"? If so, that may explain the discrepancy you're seeing relating to dump valves for all four wheels versus a shared valve for the rear. I'd also suggest you try turning off the traction control and see if the same thing happens when braking. I'd also suggest you check for proper operation of the brake lights and, using FORscan, check for toggling of the Brake Pedal Position sensor as you press and release the brake pedal.

If all four wheel speed sensors are tracking one another, and none of them drop rapidly or raise, then drop, when approaching the speed where the ABS activates, I'm at a loss for what would cause the solenoids to trigger.

Other than the pulsating brake pedal, do you notice a change in braking effectiveness? If the ABS were engaging due to a wheel speed issue, I'd expect you to notice a surge during braking due to one or more brake calipers releasing.

The ABS module is located underneath the battery tray.

-Rod

[dalem01]

I'll have to double check on the traction control but 95% sure it does not.

It's barely noticable.on the brake pedal and don't know of any pedal pulsing even with normal braking. 4 wheel disc brakes and they looked pretty good when I rotated wheels.

I goggled a bit more before retiring last night and found something similar, but not precise, suggesting maybe bad master cylinder or rear relief valve in ABS unit, allowing rear brake pressure to drop off enough for the ABS to want to pump up the rear brakes. I just happen to have her recently retired 2000 Taurus sitting out back.so I might just start swapping master cyls, then ABS units. No costs (hopefully), just time to swap, bleed, etc.

Thanks for the reply and any other ideas, I certainly appreciate it.

Dale