ABS pulses at startup and when stopped?

[Cranberry94GT]

Hello everyone.

My new-to-me '94 GT wagon (manual trans) has a strange ABS issue, and despite searching through dozens and dozens of ABS-related threads, I can't find that anyone else has had this same problem...

When I start the car, with my foot on the brake pedal, the ABS pump will kick in a few times in short bursts in a somewhat random fashion, and then quit. After that, when driving the car, it will occasionally kick in again, but only when the car is stopped and with the brake pedal held down.

The ABS light on the dash is not on, and it does not come on when the system is acting up either, but it does light up with the ABS fuse pulled so I know that the light itself works. I tried to check for codes, but I couldn't find the controller? It's supposed to be under the front passenger seat, right?


For now, I have pulled the ABS fuse, and the car stops completely fine. But I would like to fix whatever is wrong.


The pedal moves down a bit when you first step on it, so I suspect the brakes might need a bleeding. Would air in the lines cause the ABS pump to cycle like this? Is the ABS activation triggered by how far down the pedal is?

Thanks

[Cranberry94GT]

Oh, and I have read a lot about the ABS relay going bad. From what I can tell though, the car doesn't have those symptoms. The pump doesn't run when the car is off, and the battery isn't going flat when I leave it for a while.

I'm not sure that this completely rules out the relay though...

[Legacy777]

Welcome to the BBS.

You mentioned your 94 GT is a MT. I'm not sure if those models came with a MT in stock trim. Do you know if the car originally came with the MT or was it swapped in? If you don't know I can check via your VIN.

The reason I ask is because something may have gotten mixed up with the wiring.

Regarding bleeding the brakes, it can't hurt to do that, however I don't think that is your problem.

[Cranberry94GT]

Welcome to the BBS.

Thanks. I've been lurking here for years, figure I might as well sign up and participate.

You mentioned your 94 GT is a MT. I'm not sure if those models came with a MT in stock trim. Do you know if the car originally came with the MT or was it swapped in? If you don't know I can check via your VIN.

The reason I ask is because something may have gotten mixed up with the wiring.

Yep, it's a factory 5-speed. I have the original window sticker, and the 5-speed manual trans, "GT Value Group", and 4-channel ABS are all on it.

Regarding bleeding the brakes, it can't hurt to do that, however I don't think that is your problem.

Bummer. Yeah, I'm imagining taking this to the shop, and having them quote hundreds to "diagnose", and then many hundreds more to replace expensive parts.

[Legacy777]

Do you have a multi-meter, and are you knowledgeable in checking wiring and reading wiring diagrams?

[SUBYLUV871]

i have a MT to in my 94 gt. my abs light is on but i havent checked the fuse yet. ill do that now.lol my brakes pulse when i start the car with no abs light then it comes on when i drive like 20 feet. ive stomped them in the snow to see if it has abs and they dont. welcome to the bbs. i know you will get an answer. these guys have helped me alot. good luck.

[Cranberry94GT]

Do you have a multi-meter, and are you knowledgeable in checking wiring and reading wiring diagrams?

Yep, for the most part.

I've been reading through the '92 FSM (Thanks! ), but I'm pretty much stuck since I didn't find the ABS computer. So I think I'll have to find it, before I even have the right connectors to check?

[Cranberry94GT]

i have a MT to in my 94 gt. my abs light is on but i havent checked the fuse yet. ill do that now.lol my brakes pulse when i start the car with no abs light then it comes on when i drive like 20 feet. ive stomped them in the snow to see if it has abs and they dont. welcome to the bbs. i know you will get an answer. these guys have helped me alot. good luck.

Hmm... sounds similar, but I don't have the dash light. Is it normal for the ABS to pulse at startup, do you know? ("Normal" for cars which have fully functional ABS systems?)

Also, have you looked at your computer to see what codes it is blinking? And if so, is your computer located where it is expected, under the passenger seat?

[SUBYLUV871]

I checked my fuse and its good. but i asked the auto parts store to check the codes and they said it was too old for a scanner. maybe a some bs but ive asked a few shops and got the same answer. next is the abs sensor on the hub might be damaged for me. hows you fluid level? did the car sit before you got it? all your pads in good shape? maybe they need to be bled. my work truck does the same thing. holding the brake down and you can feel it pulse. when its cold the brakes are veary touchy.

[Cranberry94GT]

Fluid level is good, pretty much all the way to the top. I haven't checked the pads yet, but the brakes don't make any noise and they stop the car well.

It did sit for a while before I bought it. When I picked it up, the car had a collapsed front suspension, with the left strut spring broken, and the right strut spring broken in two places! It was still "drivable", but it made terrible noises when you turned or went over bumps and for sure wasn't safe. So I replaced both front struts right away.

But yeah, the previous owners let it sit for several months while they tried to figure out what to do with it.

[Legacy777]

The ABS computer should be under the passenger seat along the frame rail facing the door. Did you find it there? I believe there's a little flap of carpet that you can lift up and see the LED.

[vrg3]

If the ABS light isn't on, I don't think the ABS computer will be flashing any codes.

It's really weird that the ABS pump would do anything with the car stopped.

It might be worth taking a look at each of the four wheel sensors to make sure the harness is intact; if it's not, the ABS computer might be reading phantom pulses. In particular, I'd inspect the left front sensor, because the harness is bolted to the strut and maybe when the strut broke it damaged the wire.

Also take a look at the brass tone rings attached to each hub to make sure all the teeth are intact. I can't see how damage to those would cause your current problem, but it could cause other problems even if you resolve this one.

[Cranberry94GT]

The ABS computer should be under the passenger seat along the frame rail facing the door. Did you find it there? I believe there's a little flap of carpet that you can lift up and see the LED.

Found it!!

So there were two things that tripped me up. One was that the bump for the ABS computer really looks like it is part of the floor heat ducting. The other was that I was looking for a piece of carpet to lift, but the computer is actually underneath a solid piece of carpet which has a U-shaped cut in it. It's pretty much invisible when you look for it with your eyes, and you can't really "lift" the flap directly. Instead, you have to feel around and push it *IN* to find it, then grab the edge and pull it back out and up.


Thanks for the help locating it.

[Cranberry94GT]

If the ABS light isn't on, I don't think the ABS computer will be flashing any codes.

It's really weird that the ABS pump would do anything with the car stopped.

... and now that I've found the computer, unfortunately I have to report that you are correct.


I put the fuse back in, started it up, and let the car do its thing. But just like before, even though the pump was cycling, the dash light did not come on, and the ABS computer's LED wasn't blinking.

Are there any connectors you have to connect or disconnect, to get the ABS computer to blink the light? Or does it just always blink if there are any problems that it knows about?


Yes, the fact that it does it at a stop is the strange part...


I'll give the front another visual check when I have some daylight again.

[vrg3]

If your car has the ABS system I think it does, the computer just turns on the ABS warning light and then continuously blinks the code out on the LED.

Does the ABS hydraulic unit under the dash have two bleeder nipples on it? If not, I'm wrong about what system you've got.

[Cranberry94GT]

Does the ABS hydraulic unit under the dash have two bleeder nipples on it? If not, I'm wrong about what system you've got.

Ahh, yes, I forgot that there were several different ABS systems.

Mine is a Nippon unit, and it looks like the third picture in this thread:
http://bbs.legacycentral.org/viewtopic.php?t=40692

Others look like this:

[vrg3]

Okay, then, yes, what I said applies. So, like I said, I'd start by taking a careful look at the sensors and their wiring.

[Cranberry94GT]

It might be worth taking a look at each of the four wheel sensors to make sure the harness is intact; if it's not, the ABS computer might be reading phantom pulses. In particular, I'd inspect the left front sensor, because the harness is bolted to the strut and maybe when the strut broke it damaged the wire.

Also take a look at the brass tone rings attached to each hub to make sure all the teeth are intact. I can't see how damage to those would cause your current problem, but it could cause other problems even if you resolve this one.

Thanks for the suggestions.

I can't remember, do you have to pull the wheels and the rotors off to see the tone rings? Or can you check them somehow without taking everything apart?

[SUBYLUV871]

Thats funny i have a 94 gt wagon and it has the abs system pictured. not the nippon

[vrg3]

Cranberry94GT - From what I remember, you have to take the wheels and brakes off to inspect the tone rings. They're bolted to the inner side of the hub with (disturbingly soft) brass allen bolts, so they're kind of between the rotors and the backing plates. Once you get the rotor off you'll see what I'm talking about.

SUBYLUV871 - That pictured system is a Nippon system. 93-94 automatics got a different Nippon system (the "Nippon-2E" system).

[SUBYLUV871]

Oh. Lol