ABS has me sliding past stop signs!

[Melbowski]

Alrighty guys, as you read in the title my ABS is tripping balls. The symptoms are pretty straightforward, when I push the brake to come to a stop at about 10 mph or less my ABS kicks in and won't let me stop!

It makes the standard horrible ABS sound, and my brake peddle pushes back on my foot; it seems to be reacting like normal except I'm on dry roads mid-summer. After it occurs once or twice the ABS light comes on, but it resets every time I start the car.

Strangely it doesn't happen all the time, sometimes it can go days before doing it again. Also, road conditions seem to have no effect, on a 95 degree dry day, it'll kick in like the road is covered in ice. Needless to say this is a problem I'd like to fix before I hit some one or worse get hit myself when I roll past a stop sign.

Currently I have the wires for the ABS unplugged, so I'm just running with no ABS. However, with winter around the corner I'm looking for a cure.

I've searched on the forums and although I've found some people with the same problem, the thread ends after a couple posts with no solution, so I'm throwing it out here and hopefully I can get this taken car of.

From what I can tell it's either a bad wire throwing things off, a bad ABS sensor, one of my rear drums is worn and locking up, or gnomes are making magical ice under my car when I least expect it.

Extra handy info: It's a '96 Grand Am SE, 2.4L. Front disc, rear drums. Front brakes were replaced two months ago, drums about a year ago. Problem has been evident for over two years (yeah I'm slow), and car is only drivin in the winter. (I drive my 3000GT in the summer)

Sorry for the novel, but I wanted to be descriptive. Any help/comments are appreciated. Thanks in advance guys!

Melbowski

[sunrunner_pei]

I had a similar problem with my '96 Sunfire, it was the ABS module. Expensive to replace, so I just lived with ABS disabled.

[Melbowski]

Ah, it would figure that it couldn't be something cheap and easy. Where is this module located in the car? There are a couple 96-98 GA's in the nearby junkyard, maybe I can salvage a unit from one of those.

Any others have this problem? I'm going to look into the module, but just in case that doesn't work out other ideas could be useful. Thanks for the quick response Sunrunner, I appreciate it.

Melbowski

[sunrunner_pei]

Once I saw the price (Around $300 from a local shop), I decided not to pursue it any further. It was an old car I got for next to nothing as a winter beater, I didn't feel ABS was worth the expense.

[jonnythan]

Have you done a good thorough inspection of the ABS sensors on the rotors?

[RazorDX]

ABS went out on my Blazer... bad ABS module. It was a $500 part, so I just took the dash apart and pulled the "ABS" bulb. I don't know what kind of ABS these cars have, buy my Blazer with 4WAL would throw a code that you could diagnose like a CES light. I don't know about an OBDII equipped vehicle, but Autozone or someone who runs codes would.

[rixGAphx]

When this occurs, you do NOT have an ABS system that is 'engaging'; you have an ABS system that is malfunctioning.
Obviously, it should never get a signal to engage under these road/traction conditions.
And, it should actually 'work' if it DOES engage.
Frankly, irrespective of this 10-mph phenomenon, I'm very sure your system does not work at any speed under bad traction conditions.

Quit diddling around with DIY analysis of a complex electro-mechanical system that is very good at self-monitoring.
Everytime that ABS light comes 'on', the system has registered codes of what it thinks is wrong with itself.

Your problem is more severe than a simple discontinuity of a hub sensor cable, or even a hub sensor itself.
Those faults don't cause the malfunction you describe.
Other than unplugging/replugging the sensor connectors (including at the module, wherever it is) to kinda clean the pins/sockets for better contact, there's nothing you can do but throw money at parts.

True, the rear drum, particularly the passenger side for some reason, can be out-of-round and thus can cause a 'goofy' reaction from the brakes at low speed.
But that's an overall brake problem that you can easily check/repair, and should do whether the ABS is operational or not.
In my experience on my '96, the rear drum out-of-round never caused an overall ABS malfunction, so I doubt this is the cause of your ABS woes.

The biggest hint I get from your post is the comment, "It makes the standard horrible ABS sound."
Huh??
On most cars, the AbS is virtually silent when activated.
Even on the entry-level cars, like a GA, with lesser soundproofing, the ABS motors barely make an audible 'hummmm.'
So if you’ve got noise, you’ve got a major problem with the only noise source: The 3 servo motors in the black-box on the MC, with their little gear drives.
Your gear drives have stripped, causing the noise and preventing the servos from re-pressurizing the front brake lines.
Your motors are not able to re-apply pressure, so you’re only getting 30% braking force from the <unaffected> rear tires (I *think*).


Still doesn’t explain why the system is engaging initially (bleeding-off pressure, ‘cuz it thinks the front tires are near-skidding).

I would reconnect the ABS on Saturday morning, and take a short safe drive hoping the problem recurs.
When it does, I would go straight to Midas or other major national brake specialist and have them download the codes that the ABS system records.
Mebbe a wheel sensor, mebbe software, mebbe hardware with the module itself, mebbe the electro-mechanical unit on the side of the mastercylinder.
Midas will give you an estimate, take it or leave it; do the work yourself, or say screw it.
At least you'll know, and the estimate won't cost a dime.

First, make sure all the electrical connections are good: Clean, tight, shiny brite.
Both for the ABS wiring, and for the charging system (see my write-up in 'FAQ's' about battery/alternator/batt cable; I doubt this is the source of the problem, but stranger things have happened to GA's).

One good sign is that although the system is behaving goofily, the system recognizes this failure on its part and turns itself 'off' (and illuminates the ABS light to tell you so).
So we know the system's self-diagnosis is working at least to some extent.
* * *

One final word:
As you've seen, the ABS system has no specific 'fuse' or circuit, since its components cross various other circuits.
Are you having any OTHER problems with the car, mechanically or electronically, that are seemingly un-related to the ABS?
Because of the circuitry inter-relationships, something you haven't mentioned may play into this.

Hope this helps,
-Rick

PS: Analysis of ABS logic:
* There are four wheel sensors, each reporting the speed of its respective wheel to the module.
* There are only 3 antilock hydraulic circuits: one for each front tire, one for both rear tires; look at the black-box on the MC: Only thee little units.

When you apply the brakes, the system compares wheelspeed of each wheel (from the sensor) with previous readings from the same sensor, and with readings from other sensors.

Your problem is with the front brakes; they do 70% of the braking on the GA; inoperation of the rear brakes would not have this dramatic a result.
Further, to me it seems that BOTH front tires are doing this at once.
If it were only one tire, there would be strong pull (to the other direction); and you would still get 65% braking force (30% from the rear, plus 70%/2 from the other front tire).

So: Why are the relief valves/pressurizing motors operating for the front brakes, when the wheels are not even near to locking?
I’m not sure, but here are some possibilities:
1. Mebbe there are some tiny grains of sand in your dirty old brake fluid, stuck in the orifices of the relieve valves; your front brakes would ALWAYS be bleeding off some pressure, but mebbe it’s only noticeable at the end of a long application of hard braking force.
2. Keep in mind the fundamental way that THIS system works (as opposed to systems in other cars):
* The ‘puter constantly compares each wheel's speed to its speed a couple milliseconds prior.
* When you brake, the speed THIS instant is less than it was 2 milliseconds ago, so the 'puter calculates how quickly the wheel’s rotation is slowing. Repeat; repeat; repeat.
* Plot this ‘deceleration of the wheel’ on a graph, and don't let the graph get too steep:
* * * Very steep (indicating the wheel is slowing TOO quickly) means the tire is going to STOP very soon.
* * * The 'puter knows that the GA and its tires can NOT stop from say 40 mph to near zero (~5 mph) in less than about 4 seconds.
* * * If the 'puter sees a tire trying to slow this quickly, it releases some brake fluid pressure to that tire’s caliper; the wheel slows its deceleration, so the motor (one of the three in the MC unit) re-pressurizes that brake line; repeat.
* * * The GA’s 3-channel system only activates for the rear 2 wheels when it calculates that BOTH are nearing lock-up (if one locks-up, that only removes about 15% of the car’s total brake capability, so no big deal).
* Mebbe your ‘puter has a software glitch, and it just can’t make the calculations rapidly enough, or it’s otherwise screwing-up.
I can’t figure why it’s engaging ‘randomly’, though it really isn’t ‘random: It’s only at low speeds
3. The ABS *may* have an internal self-check procedure that we don’t know about. Mebbe at a relatively-safe 10mph, every 8th stop or so, the ABS TELLS the front circuits to engage (relieve pressure) so it can see how itself is doing. Then when the motors (with their stripped gears) try to re-pressurize the lines, you are in a world of hurt.
It checks itself again on the next stop, says "I’m fubar" and turns itself off.

[gir]

I've asked this before (and haven't gotten an answer) but my ABS is shot, and once the ABS went out the abs light comes on all the time I am driving. My only concern, is that the light that usually comes on for the E-brake also comes on w/ the ABS light. Is this normal, or is something else wrong?

[RazorDX]

Holy crap, Dr. Rick. You need to write a book or get a TV show.

[Pte Socks]

I agree with razor, rick, you have way too much time on your hands.

[Twista89]

I think he has all he replys like typed up and then just copy and paste for the correct problem and add where needed lol. I like his info its making me more smarter :lol:

[MantaGreen97]

Originally posted by jonnythan
Have you done a good thorough inspection of the ABS sensors on the rotors?
There is no ABS equipment on the rotors on these cars... On 96-98, on the front, the "sensor" is two-part. It consists of a toothed wheel/ring that is pressed in on the driveaxle, and a sensor that reads it which sits behind the knuckle, mounted on a bracket with an unadjustable gap between the sensor and the ring on the axle. On the rear wheels the ABS sensors are integrated into the hub (as it is for all wheels on the 99+).

Originally posted by sunrunner_pei
I had a similar problem with my '96 Sunfire, it was the ABS module. Expensive to replace...

Not really true, unless you really want a brand new one.

If the problem does turn out to be the EBCM, they are pretty cheap on eBay, so I wouldn't be afraid of it costing too much.

For the OP... you can probably get a used one for like $20-$50, no problem. Just search for "grand am ABS computer" or "grand am EBCM" or something similar. You could also get one from a yard instead though it might be a little more; but, certainly not as expensive as a new one.

Oh but be sure to get the correct EBCM, there are two of them--one for with variable effort steering and one without. If you get the wrong one you'll probably get the ABS light on and an ABS DTC will set. Speaking of that, do you know if there are any ABS DTCs currently active on your car?

[Melbowski]

Wow, and I thought my first post was a novel! Lots of great info in there though, I appreciate the amount of time that went into giving me a thorough response.

I will most certainly take your advice and try to throw a code so Midas can check it out, never even thought of such a thing. I will also make sure my connectors are good and clean before I plug them back in; lets hope this'll be quick and easy.

I appreciate the help!

[gtracing96]

Wow... i have the same problem with my abs... i have almost rearended some people because of it!

[Melbowski]

Originally posted by gtracing96
Wow... i have the same problem with my abs... i have almost rearended some people because of it!

I know it man, when it first started to happen I went to stop at a light behind a newer vette, and I couldn't stop! Luckily for me I slid and stopped with almost a foot inbetween us. I'm not sure who was more scared, me to hit a car and get a ticket, or the guy in the vette that I was about to ruin his precious.

Anywho, does your ABS work in the conditions it should? Last i knew on mine when there was actually ice on th road and I'd plug it in, it'd work just fine if I began to slide. But it would still mess me up at snow-free stop signs and such for no reason, strange no?

[rixGAphx]

Originally posted by Melbowski
....Luckily for me I slid and stopped with almost a foot in between us....Wait. You SLID????

In your first post, you indicated the ABS 'was kicking in' and that it was doing its thing and kept you from stopping quickly.
What an ABS 'does' is to release pressure and prevent skids by preventing lock-up.

NOW you're saying that what happens is you try to stop but you SKID, as in tires locked-up, rubber-track-on-the-pavement, etc.??

Which is it?

[carlover626]

I think he means that the ABS system is acting as if he is skidding, and depleating the brake operation to the problem tire (or in this case the screwed up sensor/hub/computer/whatever is wrong) as he pushes the brakes like the system is supposed to do.

I would look at getting that fixed (or turn off the ABS) before you come to another stop and hurt someone or yourself.

[Melbowski]

I appologize for my misleading choice of words. I did not skid litterally, I meant that it would not let me stop as if I was skidding. The ABS was activating, making me incapable of stopping. My first post holds the correct representation, there is no tire lock-up.

[rixGAphx]

Originally posted by Melbowski
I appologize for my misleading choice of words. I did not skid litterally, I meant that it would not let me stop as if I was skidding. The ABS was activating, making me incapable of stopping. My first post holds the correct representation, there is no tire lock-up. 'K.

[gtracing96]

Same it wouldnt let me stop either!! mine usually works when it doesnt shut itself off

[zzzz1486]

Hey Mel, I see you live in Michigan too. That might be part of your problem. On my 93 GA, I had a cracked tone gear (front passenger) which was causing the same sypmtoms you had. I think the rust that got between the gear and outer CV caused it to break. All the salt they put on the roads has really been eating away at my GA. :( I couldnt just replace the tone gear so I replaced the whole Halfshaft. I would recommend getting a new one over a remanufactured one. The first three remanfuctured halfshafts that I got at the auto parts store were messed up. Didnt want to try again and just got a new one.

Good luck

[Melbowski]

Originally posted by gtracing96
Same it wouldnt let me stop either!! mine usually works when it doesnt shut itself off

Hopefully if I get this figured out, it'll solve the problem for both of us, assuming it's not overly costly. I'd really like the ABS for winter, and not have to worry about rearending people.



Originally posted by zzzz1486
Hey Mel, I see you live in Michigan too. That might be part of your problem. On my 93 GA, I had a cracked tone gear (front passenger) which was causing the same sypmtoms you had. I think the rust that got between the gear and outer CV caused it to break. All the salt they put on the roads has really been eating away at my GA. :( I couldnt just replace the tone gear so I replaced the whole Halfshaft. I would recommend getting a new one over a remanufactured one. The first three remanfuctured halfshafts that I got at the auto parts store were messed up. Didnt want to try again and just got a new one.

Good luck

I see, how much did that run you to buy? I'm hoping it's a cheap computer I can get fixed, but we'll see what Midas says when I get it read. Depending on the cost, this could be a viable option as I'm rather mechanically inclined. I appreciate the info, if I can't get a code I'd prefer not to go into this blindly.

Thanks for all the advice guys, it's people like you that give this forum such a good reputation.

Melbowski

[zzzz1486]

This is just my two cents. Theres probably someone on here that is a mechanic, and would be better able to assist you.


Heres what i would check.

Make sure all your tires are the same size. (it happens) If this is so, you should have a sheapish look on your face, and you have found one of your problems.

Raise and support the front end. take off the tires, put the car in neutral. Turn the wheel all the way to one side to give you a better view of the wheel speed sensor and tone gear. Look for any broken or damaged teeth and cracks. You can use the rotor to spin the gear around so you can see all 360 degrees of it.. the wheel speed sensor sits very close to the tone gear and I've seen it on some junkyard cars where the speed sensor has been rubbing/grinding against the tone gear. Look for any phyiscal damage to the sensor and sensor wires.

Then turn the wheel the other way and inspect the other side.

the front tone gears and sensors might be fine. However it is a good thing to check, and a place to start. (A decent amount of abs problems are caused by these things, and you can check it yourself fairly easily).

Be safe & Good luck,

Bill

[Melbowski]

Alright after taking some time and looking around, it seems that my connector to the wheel is in bad shape. It has been sautered (man I killed that spelling) together before most likely by a previous owner. I'm actually rather suprised it lasted as long as it did.

I'm hopeful that it'll work, it might explain my stopping problem due to intermitent connection. But that wouldn't explain why it only happens below 10mph, you'd think it'd happen anytime I hit the brakes. Oh well, they need to be replaced either way.

So I hit the junkyard and picked up a set of wires that are in pretty good shape, we'll see if that cures my problem. If nothing else, it'll throw the code so I can hit up Midas, and find out what's really wrong with my beast. Thanks for all the help guys.

Melbowski

[jonnythan]

I told you to check the sensors ;)

[Melbowski]

Originally posted by jonnythan
I told you to check the sensors ;)

That you did, hopefully Occam's Razor strikes again! I'm really hoping it'll be the problem, but it wouldn't surprise me if it were only part. My car is fickle as a woman, and usually just as complicated, lol :P .

[gtracing96]

I hear ya there... lol mine too, but if it works let me know so i can look into it as well!

[Melbowski]

Alright I've got a little update. I've installed the new wires, and upon inspection of the old ones it's no wonder I'm having problems. Strangely the ones that were sautered were actually still good, meanwhile the other side was being pinched. The copper inside was broken up a bit and the insulation was slightly tore open.

I'm really hoping this cures my problem, because the way it was pinching would explain why it only messed up at low speeds. Whenever my car leaned way forward (like the little jut at the end of a stop) it would sometimes short out or lose contact.

Preliminary tests around the block have had no failures. I'll find out in the coming days if it's still messed up or not. On a side note my ecs is not working and even when abs activates (nice and quietly none the less) the low traction light doesn't come on.

Also the "ecs off" light turns off with the abs light when the key is turned to on, but once the engine is started and my check engine light comes on (rear O2, my cat is bad) it seems to turn itself off. I can't see why it would turn itself off due to a O2 sensor, but I'm not sure about anything my car does.

[rixGAphx]

When the rear O2 sensor is faulty, it pisses-off the computer 'cuz the 'puter can't monitor the cat.

So the PCM (your engine-tranny computer) switches the engine control to a very rich, limp-home, fail-safe mode called 'open-loop'; in this mode, it ignores feedback from the FRONT O2 sensor, and determines the Fuel Injection based solely on trottle position.
It also turns on the 'Check Engine Light' (CEL) to tell you, "I've gone stoopid; take me to a shop and have me fixed."
Do it, now.

When the engine is warm and operating properly, it is in 'Closed-Loop' mode.
The PCM adjusts the spark timing and the fuel injection pulsing based on data from all the sensors, but primarily based on the richness/leanness of the exhaust.
It gets this leanness data from the front O2 sensor.

How does a stoopid ol' GA do Electronic Traction Control??
It reads whether the front tires are spinning and losing traction.
It does NOT apply the brakes to reduce the spinning and regain traction.
It does NOT physically close the throttle plate (since your foot is physically keeping it open via the throttle cable and gas pedal).
Rather, the PCM merely reduces the Fuel Injection 'pulse width' so that the engine gets less gasoline, therefore loses power, therefore drops rpm, and therefore the tires stop spinning and you regain traction.

BUT, this method of controlling traction is fundamentally in conflict with the 'Open Loop', fail-safe mode of operation, which seeks to keep a very rich mixture (to prevent burning the exhaust valves).
* * *

So, by ignoring the car's scream for help (it wants you to look and see if needs a new $80 rear O2 sensor), you are:
* Running in rich, 'Open-Loop' mode;
* Rapidly destroying the front O2 sensor with the rich exhaust that is coating its sensitive surfaces.
* Slowly consuming the cat, which is trying as hard as it can to burn the additional richness and prevent pollution.
* Getting very poor gas milage, because of the rich setting.
* Getting poor horsepower/torque.
* Turning the ETS 'off', since it can't operate in the 'Open-Loop' mode.

Fix it now, since 1) It will pay for itself within 2-3 months, based on fuel consumption savings, and 2) It will soon cost much more to fix, because of other parts that are being damaged.

Hope this helps,
-Rick

[Melbowski]

Wow, I didn't know the emmisions below threshold CEL would make me go open loop. Unfortunatley a new cat isn't as cheap as $80...

I was planning on trying the old "O2 simulator" by moving the sensor away from the exaust via spark plug non-foulers. At about 4 bucks I can handle the cost. Any word on if that really works? Since we don't have emmisions testing it sounds feasable, but one never knows. Thanks for the info.

Melbowski

[Coondog]

My '02 did the exact same thing when the wheel hub/hubs went out.