Brakes

Don't have the service manual in front of me right now, but there is a sequence for the ABS light when you key on. Depending on what happens there will point to your problem. So check the manual or have someone post a copy of the diagnostics page. That will help you decide where to look.

My *thoughts* are that you may have a failing pump and it may have blown the ABS fuse. Generally I think if there is any ABS fault (obviously since there is no pressure), the light should be on. The light not on makes me think blown fuse. Why would the fuse blow since replaced the accumulator and relays? Probably excessive current draw. When you last heard the pump run, did it sound happy or did it sound like it was working a bit too hard?

If it does come down to it, you can change both the pressure switch and the pump with the unit in the car. Not easy, but you can do it. The pumps can be rebuilt or there are used ones out there. I have a slew of used systems, I'm sure some of them probably have a good pump. You can test the pump by simply hotwiring it at the connector.
 
The two fuses are both good (under the hood and in the driver side footwell area). Is there another fuse in a different spot?

Last time I heard the pump running it sounded nice and strong. Exactly how it has for the five years I've had the car.

I assume I hotwire the pump at the pressure switch?

Does anyone have part numbers for the pressure switch and the ignition switch, in case I end up need to get one or both?
 
I assume I hotwire the pump at the pressure switch?

To test the pressure switch...

See figure 5 here for the pressure switch connector pin outs: http://www.sccoia.org/articles/anti-lock-braking-system/

Unplug the ABS Pressure Switch at connector (beneath the master cylinder...see drawings at that same link) then ground pin #4. Turn key to on. Pump should run if switch is bad.

Does anyone have part numbers for the pressure switch and the ignition switch, in case I end up need to get one or both?

I bought mine via ebay - ACDelco 25530882 GM Original Equipment Brake Pressure Warning Switch, $USD122 new shipped - exact connector fit on my '90SC. Also bought the special socket used.
 
The two fuses are both good (under the hood and in the driver side footwell area). Is there another fuse in a different spot?

Last time I heard the pump running it sounded nice and strong. Exactly how it has for the five years I've had the car.

I assume I hotwire the pump at the pressure switch?

Does anyone have part numbers for the pressure switch and the ignition switch, in case I end up need to get one or both?

Try rocking the switch back/forth. Also take the steering column covers off and inspect the ignition switch. Should be no visible gap between the plastic and metal portions of the switch.

You can hotwire the pump at the pump motor by disconnecting the motor and applying 12v to one of the grey/red wire-pins, on the motor side of course. :rolleyes:, and ground to the pin immediately next to it. (OK... I'll throw you a bone here... the "flat" side of the connector.. thats a 12V pin). Don't worry about the other 2 pins, they are redundant. Im 95% sure it will run for you and then you just have to figure out why power, isn't making to the relay... the fuse block runs the motor power line to the relay. The pressure switch activates the relay.
 
I did test the connector the relay plugs into, and it read 10v DC. So this would mean that there is power getting to the relay? Which would mean the pressure switch is not faulty?

I feel like I keep remembering little details that would be helpful that l left out before.

Details so far (this is for the second abs issue in this thread; the first was resolved with the new accumulator):

Abs light (it's on, I suspect yours truly is guilty of incorrect troubleshooting), brake light, hard pedal
Fuses (CLUSTER, ABS, ABS pump, and ABS module) are good
10v DC at pump relay (for what it's worth)
No reading at four-pin plug (unless I measured it wrong :D)

Haven't had enough time to really do anything but check fuses and test connectors, and don't have money to pay someone who does. Thanks for all the help so far, guys!

I hope to do some hot wiring and stuff this weekend.
 
Last edited:
Which would mean the pressure switch is not faulty?.


If you ground pin 4 at the pressure switch connector and the pump runs, the relay is good, the pump is ok, and the pressure switch is suspect as failed.
 
Alright! This weekend's project: ground pin four of the pressure switch connector. I'll let y'all know...
 
If you ground pin 4 at the pressure switch connector and the pump runs, the relay is good, the pump is ok, and the pressure switch is suspect as failed.
Note.. Its really tucked in there. You need "E.T." fingers to accomplish this task.. :D
It might be easier to unplug the connector from underneath the car, and then insert your grounding wire from top side.
 
Note.. Its really tucked in there. You need "E.T." fingers to accomplish this task.. :D
It might be easier to unplug the connector from underneath the car, and then insert your grounding wire from top side.

Agreed and good idea.

I find that removing the ARC shroud helps the overall process. First time is difficult, but like so many things on an SC, it's near trivial once you've been around the tree before. The hard part is not breaking the clips on the decades old connector ;)

I'd go after the ignition switch before I'd debug the pressure switch, BTW.
 
I did test the connector the relay plugs into, and it read 10v DC. So this would mean that there is power getting to the relay?
10v DC usually means a loose/frayed/broken wire or a loose/dirty connector spades. Wiggle and push the test leads around fishing for 12V (battery voltage). It also could be a loose fuse, a loose ignition switch, corrosion on electrical contacts, etc..

most of the time, thats SORT OF (not always) what low voltage is telling you.
 
Went out last night and wiggled the ignition switch and bingo. Problem solved. Played around some more this morning; pumping brakes, etc., same results. So... buy a new one and install it? Or leave the steering column covers off and wiggle the thing every time I have an electrical issue and hope it solves it? :)

Also: I noticed that there is a wire hanging loose with part of a broken connector on it, and the other part looks to be fixed to the ignition itself, on the side facing the driver. The broken edges all line up, but the wire doesn't completely reach the ignition and the rest of the connector there. Thoughts? I'll try to post a picture when I get home.
 
These switches don't last forever, they are readily available, aren't that expensive, and not that hard to replace...you will need the proper torx, tho.

I'd treat the car to a new one in any case.

Will wait for the photo on the wire, but it might help narrow things down if you can say how thick and what color, thanks.

>So... buy a new one and install it? Or leave the steering column covers off and wiggle the thing every time I have an electrical issue and hope it solves it?
Or trade it for mule and shoot the mule...
 
Last edited:
Went out last night and wiggled the ignition switch and bingo. Problem solved. Played around some more this morning; pumping brakes, etc., same results. So... buy a new one and install it? Or leave the steering column covers off and wiggle the thing every time I have an electrical issue and hope it solves it? :)
Eliminate the known headache and replace it. :)
 
IMG_4593.jpg

This is the only one I could get to upload (yes, I tried to upload the from my phone).

You can see the wire, just your sorta standard 16g automotive wire, gray with a red stripe, and it looks like it, at one point, butted into the fractured connector in the ignition.
 
Ah, yes, that's the contact that tells the chime if you leave the key in and open the door.

I had to source one off a donor at the wrecking yard. As I recall, you need to remove the lock cylinder to slide it out to the right...other end is obvious, I think. To remove the lock cylinder, insert the key, rotate to 'on', then look underneath for a small round ball - push in on it, then slide the entire assembly out to the right.
 
Last edited:
Well, we're back in business! Got the new switch, took a little drive, smoked several of the local rods, and all is well so far.

I declined to repair the chime wire for now.it now makes sense that I never heard the chime when the key was still in and I opened the door. Perhaps when I have more time...but then there'll probably be something else! When something else comes up (let's face it, it's an aging car; things will break), I will return, and hopefully in a new thread about a different issue! I'm a little tired of seeing that abs light, though I'll admit I have gained a ton of knowledge from this little issue.

Thanks again, folks!

Here's a photo of the car itself, just for kicks.

IMG_4129.jpg
 
Looks good.

My chime module somehow unplugged itself a couple years ago.. :D ;) I run the risk of leaving the lights on, but at least it doesn't annoy me with complaints about the seat belts and I can play the stereo with the doors open now.
 
Back
Top