[dusteravenue]

I have a 1991 s15 Jimmy 4x4, 4 door 4.3l auto.

It has been driving well. ABS has been working. Now that there is snow and it is slippery out I braked really hard 2 days ago around a corner, I could feel the brake pedal pulsing. Then when I let off the brake, the ABS and Brake warning lights came on. Brakes still work fine but no ABS.

I got the ABS Code 63 - Solenoid Valve relay fault.

A few months ago I replaced the right rear wheel cylinder and the brake line from the center of the differential to the brake cylinder. I only bled the rear brakes and it has worked fine since. Could this be related?

I checked the brake fluid and it was pretty low. I topped it up but wonder if it sucked a bit of air?

While jumping the A & H terminal of the ALDL port the ABS module hums/vibrates for a couple seconds. Does that indicate the unit still works?

Suggestions?

 

[Rhotpursuit]

I’d be questioning why it was low.

 

[dusteravenue]

I’d be questioning why it was low.

It was around the MIN level, but when I bled the brakes I'm fairly certain i filled it up more. But I also found the rubber inner boot of the reservoir pushed down into the fluid. But no sign of leaking.

 

[oldeerslayer]

Sounds like you sprung a leak somewhere. When you have recently been driving in snow it's hard to spot a leak. It's normal for the rubber gasket in the master to be drawn down when there is a sudden loss of fluid because a slight vacuum is created when that happens.
My 02 did the same thing 4 days ago. I can see where the line from the ABS to the line over to the front passengers side is leaking. Was gonna fix it this coming week by replacing the rusted thru line. No longer available, so I'll have to make one. I'll use Nicop line which will never rust and my double flaring tool. But it's gonna have to wait as they're talking single digit temps all next week. (around -15°C)
Symptoms are exactly the same. Returning from town after a 7" (18cm) heavy wet snow fall. Hit the brakes and no more pulsing and both brake and ABS lights came on. When the brake light is triggered by a leak the ABS is shut down causing it's light to come on. Checked fluid and it was low. Pulled it into the barn over some carboard, added fluid and pumped the brakes half a dozen times. Fluid was dripping right below the leak. S10's are famous for leaking under the drivers side between the firewall and the rear wheel. That 1/4" long line to the back has 2 or 3 places it likes to rust thru. I had replaced all of the rear lines last year. Guess this year it gets fronts.
If you see some dripping, stick your finger in it and taste it. If it's water dripping no taste. If it's brake fluid you'll know immediately. YUCK!

 

[dusteravenue]

So the issue has been resolved for now...

I put the Jimmy in the garage over night and it dried off. I checked for leaks and found none, pumped the brakes 10x and looked again. I didn't find any leaks.

Then I used a wire and jumped the A & H terminal while pumping the brakes about 5x. Each time I jumped the terminals the ABS unit pulsated.

The ABS and Brake lights went out and the ABS is working again. So problem solved but still no idea of why it happened.

 

[oldeerslayer]

Glad you got it fixed.
Got my new line built and on and will finish the bleeding tomorrow.