Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Ford Explorer Community - Maintenance - Modifications - Performance Upgrades - Problem Solving - Off-Road - Street
Explorer Forum Covers the Explorer ST, Explorer Sport, Explorer Sport Trac, Lincoln Aviator, Mercury Mountaineer, Mazda Navajo, Ford Ranger, Mazda Pickups, and the Ford Aerostar
Since I bought my Ex I have had a problem where the ABS would activate when coming to a stop. Recently I decided to replace all of the wheel speed sensors to solve my ABS problem however the ABS problem continued at about the same frequency as before. When I have the vehicle on jacks next I will clean the tone rings with Isopropyl alcohol but I believe that the problem might be located elsewhere. I had an ABS light on during my drive to Fort Collins earlier this week but not since. I am generally unfamiliar with ABS systems, and I am wondering what some methods are that might be able to locate which wheel is producing the weak signal. Since replacing the sensors I have also cleaned the connectors to each of them, but to no avail. If the ABS light illuminates again I will read the codes with my OBD1 reader.
Heh, I wrote too much, should have suggested a forum search but here it is anyway:
Take everything I've written below with a grain of salt, as I have no hands-on experience with '93 and am making some assumptions based on my '98. Most of it is applicable and the techniques are the same.
The general operation is as the wheel spins, the teeth on the tone ring need to pass very close to the sensor which has inductive wire core, and when this happens it produces a very low AC voltage signal that is set to the ABS controller, to operate the ABS pump during braking events where a wheel shows no signal as evidence of it locking up, and the controller turns on the dash light if a problem is detected. The controller itself can fail but this is less likely, especially with it intermittent and happening when coming to a stop which is sort of the opposite, that the controller is doing what it senses it's supposed to do.
Dirty tone ring (contaminated with metal particles in the grease if internal) or rust /other-goop if external, or spacing, or wire damage, or connector corrosion, any of these can cause a weak signal, that gets weaker still the slower the tone ring (wheel/vehicle-speed) spins.
Is this a 4WD vehicle with your front wheel bearings integrated into hubs and speed sensors that sit in the hubs?
I know you mentioned cleaning the tone rings which if external means it is 2WD? Though in theory someone could try to clean the tone rings internal to the hub on a 4WD. If the tone rings are external they may need some rust removal. If internal to a hub, you may need to just pick or wipe chunks of grease out, and if you need a solvent, a little gasoline would work better than alcohol to dissolve the grease. If cleaning an internal tone ring works, your hub bearing is probably shot, contaminated metal particles in the grease, and the hub still needs replaced.
If the tone rings are external, have you laid eyes on them yet? Could be one is rotten away or dislodged.
You can test the sensors making a signal by spinning the wheel and measuring at the sensor pigtail connector with a multimeter on low AC voltage mode. If you note the wire colors on the wiring harness plug, that plugs into the ABS sensor connector, then you can also unplug the connector to the ABS controller on the ABS module pump (where all the hydraulic lines go from the brake master cylinder) and measure for low AC voltage with wheel spinning to see if the signal is making it all the way to the ABS controller.
You can test each sensor's internal coil by measuring resistance across the connector pins, should be a few hundred, possibly about 420 ohms +/- ~10%. This can be done either at the sensor connector or at the unplugged ABS controller connector. The rear sensor (Rock Auto suggests that it's on the rear differential) can be tested the same ways, but as far as I know, it's supposed to have a different resistance value than the front wheel sensors. I just don't remember what that resistance value is supposed to be.
On my '98 with 4WD, I had the same problem of ABS activation coming to a stop, and I replaced a sensor, cleaned the hub internal tone ring a little, and that worked for a little while but then the issue returned, so I replaced the entire hub and that fixed it... then close to a year later, the issue came back because my other front hub started to fail.
One other thing you can do is take your hands off the steering wheel (in an area safe to do so of course) and when coming to a stop with ABS activating, see which way the vehicle pulls if it's a front wheel signal issue. It should pull opposite the direction of a bad wheel sensor signal, so if the left wheel signal is bad, it will pull right and vice versa if the right wheel signal is bad.
I'm suggesting that the front wheels sensor is more likely than the rear one... wherever it is, unless there is wiring damage causing intermittent shorting. A lot can happen in 30 years, including general wear and in my case, I think an especially potholed and half patched stretch of road, wore my front hubs out a bit faster, but it's not uncommon to need the factory hubs (or front bearings if RWD) replaced after 30 years.
I just noticed something strange. I looked up the hubs for a '93 on Rock Auto, and it only lists one part # available, an SKF BR930252. Seemed a little pricey at $140 but maybe not with inflation and it's at least a non-generic brand, then I realized it's supposed to be compatible with my '98 too which also has a lot more other hub makes listed, so why aren't they also listed for your '93 unless this SKF is not really compatible with both a '93 and '98? The 4WD speed sensors themselves definitely look different. Probably something wrong with Rock Auto's parts compatibility one way or the other.
Brake & Wheel Hub Parts and More for Your 1993 FORD EXPLORER at Reliably Low Prices. Fast Online Catalog. DIY-Easy. Your Choice of Quality. Full Manufacturer Warranty.
Brake & Wheel Hub Parts and More for Your 1998 FORD EXPLORER at Reliably Low Prices. Fast Online Catalog. DIY-Easy. Your Choice of Quality. Full Manufacturer Warranty.
www.rockauto.com
This post is subject to editing at any time to improve the quality or accuracy of the content.
Here are some answers to the questions which you have presented:
1. It is indeed a 4wd, however the tone ring visible when the wheels and rotor plate are removed.
2. I completely removed the hub/rotor assembly when I changed the sensors and gave the tone rings a shot of brake cleaner but I believe that Isopropyl alcohol would probably do a better job at removing the outer layer of grime.
3. There is no noticeable brake pull when the ABS activates.
4. All of the ABS sensors on the vehicle are new, which in combination with how intermittent the problem is makes me believe that it is some issue with the wiring from the ABS module to the connector.
Thank you for the advice on the resistance value of the coils, and the ABS connections. What would be an approximate voltage when measuring the sensor outputs with a voltmeter?
Voltage varies by speed, just compare the left side to the right. It's fractions of a volt, AC.
I think I understand now, your tone ring is built into the back of the rotor? If you can't get it clean enough, might have to replace the rotor, or check sensor clearance as you want it as close as possible to the tone ring, without rubbing.
If there is grime, you probably ought to use a toothbrush along with your choice of solvent. Brake cleaner seems ideal for that if you have it, or even plain old hot detergent solution if it's just road grime.
Does the abs fault happen any other time than very slow, right before stopping? If not, I'm thinking it is a weak signal because a wiring fault would tend to show up at faster speeds too, unless the momentum loss is causing a wire to shift positions and then short out. How intermittent is it really, I mean does it happen practically every time you slow to a stop? Mine didn't at first but pretty soon it was every time. It still seems possible to me that worn out hub bearings could cause enough of a shift in relative rotor position to cause this, so I would check for bearing play.
The thing about there being no pull is then it must be pretty close to applying even braking force/duration to both front wheels, so I would put more focus on the rear sensor which "might' be in your rear differential.
You can use a multimeter to check resistance from the ABS controller connector, to the ABS sensor connector, on each same colored wire. Should be under 5 ohms, ideally approaching 0 ohms but if it's intermittent it could be hard to find. Worst case is you could replace that run of wire but I wouldn't jump to that conclusion just yet, and as mentioned above, it might be the wire run to the rear sensor since it doesn't pull to either side.
So far it only happens when coming to a stop, but the reason I believe that it is something to do with the wiring is because it is about 50/50 whether it will happen or not on a given drive. On trips where it occurs, it might even activate multiple times when slowing down for a stop light. It is also entirely possible that a relatively minor wiring problem would cause intermittent failure with such a low AC voltages.
Did you do any of the wire resistance checks yet? I'd do that before proceeding further.
Since it doesn't have OBD2, there's no way (AFAIK) to get real-time data on which sensor (including its wiring) isn't working when ABS triggers, except hands-on analog, to rig up a pair of jumper wires from the ABC module's wire harness connector, to a multimeter so you can measure the voltage dropout when ABS triggers. Whether you'd be able to do this just spinning the wheel by hand (won't need a helper applying the brakes), or need to drive it because some wire is shifting around, I don't know since it is intermittent.
Another option is run new wire from each sensor to the ABS module connector. You could make it permanent one at a time, hoping you get lucky on first or second try instead of having to do all three, or do a temporary run where you only buy one ABS sensor connector, unplug the factory connector temporarily and use the one you bought, and the other end, back probed into the respective contacts on the ABS module connector. You could possibly get the connectors from a junkyard donor vehicle to save some money. I can't tell you which model years (and even other Ford models besides an Explorer) used the same ABS connectors as yours.
The final option I can think of, and at least drive safer stopping till this is resolved, is just pull the ABS fuse and not have ABS at all. AFAIK your model year doesn't lose the speedometer doing so. However if that sets a code and the dash light comes on, you might need a scan tool to clear that later, instead of it going away when the problem is resolved. That happened to mine, I had pulled the fuse, put it back in, but had to clear the code with scan tool. Maybe it would have gone away eventually by driving a while but I just wanted it cleared immediately to be sure the repair was finished. Different model year vehicle, so YMMV.
I'm still not entirely convinced that it is a wiring problem. Having the ABS light on continuously would be more evidence of that, and you stated it did for a while, but now with it not doing that, yet still getting ABS false triggering, it seems more like too low a signal being generated by the sensor do to low wheel speed in combination with a bad sensor (even if it is new, sometimes it happens though rare), bad sensor positioning (too far or misaligned from tone ring), tone ring excessively fouled with much or rust), or tone ring shifted position, or wheel bearings shot causing excessive sensor tone ring gap.
Well... It seems like the problem has subsided over the last couple of days. The other day when I was on my lunch break at work I managed to remove the outer part of the connector on the ABS module to expose the wiring but did not have enough time to completely remove the connector. After putting the backing piece back on the connector, I was planning on inspecting the sensor when I got back from work but was preoccupied. Since then I have not had the ABS module pulse on my commute to work, and I definitely have my fingers crossed that the problem is fixed for the time being.
