ABS kicks on for no reason

[CurseTheSky]

2001 Ford Explorer Sport Trac, 150k miles
4.0L SOHC, ABS, front discs and rear drums

For whatever reason, when coming to a normal stop at a stop sign, the ABS occasionally kicks on. This is on dry pavement with good tires.

It seems to only happen for the first stop after starting, so it may have something to do with temperature. I also never noticed the issue before the Winter.

Any ideas of things I should check? I will be checking the obvious (fluid level, pad wear, etc.) when I get out of work, but if you guys could give any other suggestions so that I can knock out as many birds as possible, I'd appreciate it.

Thanks.

 

[Jimzz]

Check your rear drums. Very common on trucks with rear drums that the rear will grab a lot harder when cold.

My truck can lock up the rear when cold. I need to look and see if its time for rear brakes.

 

[phucheneh]

You sure it's ABS activation?

This is usually the result of different size tires. Hard for it to be a bad sensor; either they fail completely (or get the wires cut) or they keep sending a signal, even if it's a weak one.

Could be the ABS module itself, but again; unlikely. I would see if you can find someone to check for ABS codes.

 

[kornphlake]

Could be a short in the ABS wiring harness. My car started doing the same thing recently, apparently it's somewhat common for W-body GM vehicles to short the wiring harness where the wires pass through the wheel well.

 

[phucheneh]

Could be a short in the ABS wiring harness. My car started doing the same thing recently, apparently it's somewhat common for W-body GM vehicles to short the wiring harness where the wires pass through the wheel well.

That caused unwanted ABS activation? Definitely odd, if so...the ABS ECU must not be terribly discerning about the quality of it's signal.

Wheel speed sensors are usually going to generate a smooth waveform, with a frequency that varies with speed. Some are square wave, but the function is the same...just analog 'pulse generator' versus digital 'hall effect' types.

Anyhow, assuming there is only ABS function (no traction/stability), all the ECM is looking for is a wheel that stops moving- a wiring issue can cause the signal to stop being sent, as if the wheel has locked...but when the ABS starts working and sees that it is having no effect on the speed of that wheel, it should relent and set a DTC.

I suppose if the short is very intermittent and only occurs for a brief moment, you could get random activations of one wheel (or both rears, since IIRC that Explorer is 3-channel, not 4). That would be...pretty scary.

The best place to start would be to determine exactly what wheels are being acted upon. How often is this happening, OP?

 

[wirednuts]

my ranger (99, so basically same truck as yours) does that when the brakes are bad. if you have to push the brake pedal down a little before the truck starts to slow, something is wrong with the brakes and it can make the abs system activate sporadically at slow speeds. its really annoying, because its like youre brake checking people. many times the tires will just lock up for a second too, because something about mushy brakes makes the abs system freak out...

 

[phucheneh]

my ranger (99, so basically same truck as yours) does that when the brakes are bad. if you have to push the brake pedal down a little before the truck starts to slow, something is wrong with the brakes and it can make the abs system activate sporadically at slow speeds. its really annoying, because its like youre brake checking people. many times the tires will just lock up for a second too, because something about mushy brakes makes the abs system freak out...

What do you mean by 'brakes are bad'? Pads/shoes are worn?

I'm honestly just curious; this is a new one for me (usually ABS complaints are outright part failures, ripped wiring harnesses, or mix'n'match tire-related).

Just doesn't make much sense that any standard mechanical or hydraulic problem related to the service brakes would cause ABS issues. Aside from the ABS system itself, the only other common issue I can think of is bad wheel bearings. That causes the reluctor on the hub or axle to wobble and muck up the signal.

 

[wirednuts]

remember, these are fords so sensors are galore and they can all effect actual operation.

in my case, its when the brakes have a leak. like in the rear- either a leaky cylinder or the shoes springs are broke and there is no pressure on one wheel. it causes weird braking action, naturally, but it also confuses these abs systems... i know most cars arent effected by this, but these fords seem to be. when my brakes are proper i dont have any issues, the abs system works really well (winter driving!)

 

[phucheneh]

Weird.

Perhaps there is something in the hydraulic unit that senses the pressure loss, and activates the ABS pump motor to try and compensate.

OP didn't mention the pedal feeling odd. But we'll see what he finds when he does a visual inspection.

Curse - remember than the fluid is supposed to be 'low' if the pads are worn. Just being below full doesn't indicate a leak, since the level goes down as the brake linings wear. But it should be above the minimum as long as the you've got a decent bit of material left on them. Hard to judge fluid loss sometimes, because people like to 'top off' a sealed system.

 

[wirednuts]

most people dont know what the brake pedal should really feel like... they just know how theirs feels.

heck, even i forget how tight my brakes should be. sometimes i have to stop and think because it happens so slowly over many weeks... you just dont notice it.

 

[phucheneh]

most people dont know what the brake pedal should really feel like... they just know how theirs feels.

heck, even i forget how tight my brakes should be. sometimes i have to stop and think because it happens so slowly over many weeks... you just dont notice it.

You can also fake yourself out, though...sitting there at the stoplight, playing with the pedal: 'hey, if I push REALLY hard I think I can bottom it out...what's that about...'

When in reality you're just overthinking it and creating a worry that isn't there. If you ever created that much hydraulic pressure while driving, you'd go skidding in an instant.

Stuff like this is actually one area where I (kind of) trust people. As far as the inputs are concerned, they know how their particular car should feel. I might get in it and notice the noisy front tires, the bad axle/hub bearing in the rear, the vibration in the floorboard...all this shit I've just become almost annoyingly attuned to*.

But brake pedal is one thing where I've often even defaulted to someone else's opinion. E.g. I replace a hydraulic unit or master cylinder (something 'far up' in the system), thoroughly bleed the brakes, go for a test drive...on multiple occasions, the next thing I did was go find a buddy and say 'hey, drive this car and tell me what you think.' 99% of the time they came back and told me the brakes felt fine; 'that's how they all feel.' I was just obsessing over the pedal feel, worrying that the customer would think it had gotten mushier. Never had one complain of such.

Anecdote aside, basically: When it comes to something like brakes, I've just found that sometimes the layman (not 'enthusiast' or anything; just an A-B person) is the best judge of normal feel.


*if you wanna be an NVH (noise/vibration/harshness) diagnostic god, work for a luxury car dealer...but it's not as glamorous as it sounds. Everytime you're in a car, it's like you're watching a movie that revolves around your profession. 'That's not how that's supposed to work, dammit!'

 

[shekondar]

The problem is...it's a Ford.

My last truck was a 2000 Ranger (front disc/rear drum brakes with ABS on the rear only) - it had the worst brakes of any vehicle I've driven. Its rear brakes would usually grab and lock up the first few stops after it had been parked, but I never noticed the ABS kicking in. The strange thing was, it was only one side that was locking up. I think part of the problem was with the self-adjusting mechanism on the brakes - the problem seemed worse any time I used the parking brake (which I believe is what activates the self-adjuster on Fords).

It also had a nasty habit of kicking the ABS on if I happened to hit a bump while trying to stop - apparently it would make the back wheels lose contact with the road, which would make the brakes grab a bit too much and kick the ABS on, which would then suck power from the front brakes.

 

[*kjm]

I had one of the ABS sensors go bad on my 2002 F150 in the front and it did the same thing. The fix was to replace it or pull the fuse for the ABS.

 

[MoMo62]

my 2006 Pontiac Grand Prix has 152,00kms on it. I just had my front breaks and pads replaced, along with a wheel bearing. Ever since, my ABS light comes on and goes off, consistently. What's going on here??? Help please..........

 

[LTC8K6]

my 2006 Pontiac Grand Prix has 152,00kms on it. I just had my front breaks and pads replaced, along with a wheel bearing. Ever since, my ABS light comes on and goes off, consistently. What's going on here??? Help please..........

Take it back?

 

[Torchedrfr]

It's your brakes!!! More specifically it's your front brakes. If your passenger side has more meat/life than your driver, it will trigger the ABS. Same goes for if the driver side has more meat than the passenger. Also, if one of your rotors are more worn than the other, that would cause your ABS to crap on you.

Note: your ABS light will not, necessarily, come on in this instance. But if your amber colored abs light comes on you may have a seperate issue. Infact, if your amber colored ABS light is on, that same ABS light will turn off when your Anti-Braking-System activates. So if you had a previous ABS (light on) issue, the light will turn off when you feel the bumpy grindy braking system activate.

So, if your Anti Braking System Activates withought an ABS light on, you have a brake pad, brake caliper or brake rotor issue 😁👍

 

[Torchedrfr]

2006 Grand prix lol.

 

[MixMasterTang]

I am sure he appreciates your feedback, but I think after 3 years, 3 months and 28 days he has probably either figured it out or wrecked into something!

 

[Torchedrfr]

I am sure he appreciates your feedback, but I think after 3 years, 3 months and 28 days he has probably either figured it out or wrecked into something!

The answer is for the next poor soul who poured money into the endless abs crap shoot and has resorted to the WebMD for cars👍👍👍

 

[Torchedrfr]

my 2006 Pontiac Grand Prix has 152,00kms on it. I just had my front breaks and pads replaced, along with a wheel bearing. Ever since, my ABS light comes on and goes off, consistently. What's going on here??? Help please..........

2006 Grand Prix
Speed sensor or your hub is out of alignment!!! Not your brakes. The shop that did your job may have accidently stretched your speed sensor wire when removing your caliper, which can cause them to fail. Or, your new hub was installed incorrectly/misaligned or already has a new issue.

PS: not all new parts come out of the factory in working condition!

 

[Peter06412]

I know exactly what it is, it's the release valve for the abs in the caliper it got a bit of gunk stuck in it when they were beading the brakes. Or from when they pushed the calipers back in to put new pads on. It can also just happen if gunk gets caught in it now one needs to have done any work to the vehicle for this to happen. It is a common problem in 2000 GMC. I had the same problem with my truck before. Hope you resolved the problem by now. You have to change the valve or the calipers depends where the valve is located. Also you should change your brake fluid and check all brake lines you probably have a bad line somewhere.

 

[boomerang]

A thread resurrected for posts by people who haven't got a clue what they are talking about.

 

[LTC8K6]

A thread resurrected for posts by people who haven't got a clue what they are talking about.

Ah yes, the old ABS Bleeder Relief Valve.

Need to clean it and then lube it with genuine GM ABS Bleeder Valve Oil.

 

[freeskier93]

Ah yes, the old ABS Bleeder Relief Valve.

Need to clean it and then lube it with genuine GM ABS Bleeder Valve Oil.

And this is just for that new Anti-Braking System, right?

 

[leper84]

Three times a necro, damn. Now I wanna know what OP did to fix it. Shoes?