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ABS Question


rlalle
09-27-2011, 10:38 AM
The ABS comes on everytime I stop on my 2001 Ford Explorer Sport Trac. This morning I had a scan tool put on and it showed all sensors working properly. The ABS Light never comes on when this happens. It has been doing it for some time now and I am about to go with new front pads and rotors. One weird thing I can be coming up a steep hill to a red light and when I slow down enough without touching the brake the ABS comes on. Not the light just the pulsating. That seems weird to me. Any input on this would be appreciated. Thanks.


Rick

shorod
09-27-2011, 03:46 PM
Does the scan tool you connected enable you to monitor the individual speed sensors speeds? If so, carefully watch them as you come to a stop and see if one of them drops to 0 mph at the same time the ABS control unit engages. At approximately what speed does the ABS unit engage at? Does your Explorer have traction/stability control (RSC or AdvancTrac)?

-Rod

rlalle
09-28-2011, 12:18 AM
Wow i had no clue there where 2 different Abs applications Rod,,,that i will check into. ABS kicks in at around 5 MPH on a nice easy stop. What gets me is how it can come on while i coast to a stop on a step hill without touching the brake pedal. Here in Pa we gots lots a hills,,,smiles

shorod
09-28-2011, 07:57 AM
I've driven through the Delaware Water Gap a couple of times, them some big hills!

The fact that your ABS activates even when the driver is not applying the brakes would lead me to suspect that you have a wheel speed sensor that is registering something odd, like either a missing pulse or abnormal pulse spacing. A missing pulse could be due to a missing tooth on an ABS tone ring, abnormal pulse spacing could be due to a crack in the tone ring that has caused a gap between two teeth. Either of these conditions would likely show up on a scan tool that can monitor the ABS system and has a pretty high sampling rate. If you are not seeing anything on the wheel speed sensor readings of the scan tool, check the wheel solenoids to see which one (or more) is (are) activating when coming to a stop.

On two occasions I worked on a car that the had problems with ABS sometimes activating when coming to a stop with brakes applied. On the one that I actually witnessed with the scan tool connected, it would happen at 3 mph but only on damp days. The RF wheel speed sensor would get to 3 mph then drop to 0 mph while the other three hit 2 and 1 mph before going to 0 mph. Neither car had traction control or stability control, one was a 1997 and the other a 2000 model year, both were Chevy Malibus, and both had issues with the RF wheel speed sensor. On the 1997 that I worked on, I ended up having to replace 18 inches of sensor wire between the connector for the wheel speed sensor and the wiring harness. Apparently the insulation on the wire from the factory was somehow damaged and allowed moisture to get in to it. The copper strands were black and nasty from the connector to at least 12 inches up. At 18 inches the copper was clean enough I could at least solder to it. I soldered in a new length of wire and used adhesive-lined shrink sleeving to protect my splice. I told the owner of the 2000 that he'd probably run in to a similar situation (never heard if he fixed his or not).

-Rod

rlalle
09-29-2011, 01:37 AM
Thankyou Rod for your time. Ill be taking it apart this weekend and ill surely let you know what i find.

Rick

rlalle
09-29-2011, 06:06 AM
Just wondering if i can pull the ABS fuse as a last resort or will it effect something else too?

shorod
09-29-2011, 07:58 AM
According to the factory service manual, there are four fuses that provide power to the ABS system, F2.11 (7.5A), F1.6 (50A), F1.28 (30A), and F2.14 (10A). Fuse 2.11 in the Central Junction Box provides power for the ABS light in the instrument cluster, along with several other lights and dingers. The other fuses (1-series fuses in Battery Junction Box, and 2-series in Central Junction Box) provide power only to the ABS module. It would see you could unplug the ABS computer or pull those 3 fuses as a last resort without affecting other devices, but I wouldn't swear by that and would certainly only do that as a last resort.

-Rod

rlalle
10-03-2011, 07:19 PM
Update/ On Saturday I replaced front rotors and brake pads and I really did need them. Right side was 2/32 bonded and left was 1/32. Left front rotor wasn't braking on the back side and the outer side of the left front rotor showed black worp marks. Thought for sure this would fix the ABS but in road testing it didn't. Something I neglected to mention is when the ABS comes on at 3-5 mph the wheel pulls to the left. Back to the drawing board.


Rick

shorod
10-03-2011, 08:23 PM
The pulling to the left would suggest the wheel having the issue is on the right side of the vehicle, and most likely the right front. You could try cleaning the ABS sensor by removing it from the hub/knuckle and spraying it with some brake cleaner. I'd also suggest you carefully inspect the sensor and the tone ring looking for any contamination, cracks, or chips.

-Rod

-Rod

rlalle
10-05-2011, 01:49 PM
Ok, looks like ill be replacing the right front hub bearing cause the sensor and tone ring are part of the bearing assm. I just might have a scan tool put on it again just for the hell of it before i do the bearing,,,Hey i got a question,,,is the bearing pressed on the axle shaft or is it installed on splines. If its pressed on i dont have a press so i might have it done.

Thanks again
Rick

shorod
10-05-2011, 02:19 PM
I'm not sure on the assembly. I wouldn't be surprised if the hub is pressed in to the bearing and the hub is splined (assuming you have 4WD) and the hub/bearing assembly is bolted to the knuckle. If that is the case, and if the hub assembly is not severely corroded to the knuckle, you could probably replace this yourself if so inclined. I'll try to remember to check the service manual tonight to see how this is configured on your Sport Trac.

-Rod

shorod
10-05-2011, 08:55 PM
According to the service manual, the bearing is part of the hub. There is a spline in the hub/bearing assembly, assuming you have 4WD. You need to remove the spindle nut, ABS sensor, dust shield, then the three bolts holding the hub/bearing assembly in to the steering knuckle.

-Rod

rlalle
10-10-2011, 09:05 AM
For now the underhood 50 amp fuse is out and the brakes work like they should,,,that will bide me some time before i get back to it,,,and ofcoarse the ABS light is lite,,,

rlalle
10-11-2011, 08:10 AM
So now 2 days later after disconnesting the 50 amp ABS fuse the damn Check Engine Lite came on,,,i swear its cause the ABS fuse is out,,,gimme a break !!!

shorod
10-11-2011, 03:33 PM
Do you have a scan tool to allow you to pull the powertrain diagnostic codes? If not, some of the chain auto parts stores offer this service free of charge.

-Rod

rlalle
10-12-2011, 08:04 AM
Ok so yesterday after work i put the 50 amp fuse back in and soon as i started it both lites went out,,,so now im back to abs comes on at 5 to 3 mph. Yes ill have a friend scan it soon as he can and im hoping to see a wheel sensor thats not working. was a good experment anyway,,,now i know the ABS Light can turn on the Check Engine Light too,,,haha

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