1993 EBC4 C1500 Suburban

[Strages]

So, I have been living with my ABS and Parking Brake light on for some time.
Research online suggests this is potentially a huge headache.

So i have pulled codes 61 (RF, reset switch), 62(LF, reset switch), and 12(self diagnostic successful). It seems that they[61,62] may all be hard codes. As the two lights(ABS light and Parking Brake light) never, ever turn off.

For the year the truck had sat while rebuilding an engine for it, the hoses had collapsed and the calipers stuck. Perhaps this is an indication of possible contamination in the brake unit?

Any idea of how to diagnose this? I dont really know where to start, and all my buddies would "cave-man" the brake sytem with a proportioning valve if it was them.

 

[Schurkey]

Perhaps a moderator will move this thread out of ENGINES and into Axles + Brakes.

So, I have been living with my ABS and Parking Brake light on for some time.

"Parking Brake" light?

Are you talking about the three-system "BRAKE" warning light, that can be triggered by any one or a combination of
1. The park-brake pedal switch,
2. The Safety Switch in the Combination Valve, or
3. The ABS unit

The first thing you need to do is figure out which--or how many--of those is actually causing the BRAKE light to glow.

Research online suggests this is potentially a huge headache.

Yup.

So i have pulled codes 61, 62, and 12. It seems that they may all be hard codes. As the two lights never, ever turn off.

"12" is normal.

What are "61" and "62". Don't make us look them up.

For the year the truck had sat while rebuilding an engine for it, the hoses had collapsed and the calipers stuck. Perhaps this is evidence of contamination in the brake unit?

Absolutely evidence of contaminated brake fluid.

You need to TOTALLY flush the brake fluid, including what's in the ABS unit. This will require a scan tool, and "special tools", potentially home-made. See attached instructions.

Any idea of how to diagnose this?

FIRST, find out what is and is not working in the brake system. You already know about the calipers. What about the wheel cylinders? Pads and shoes? Rotors and drums?

You haven't told us whether this is 2WD--which would require occasional front wheel-bearing repacking and adjustment--or 4WD which wouldn't (but could require replacement of the hub/bearing assembly.)

1993 Suburban should have the EBC4 ABS unit. Far as I know, the front wheel speed sensors are exposed. Easily knocked-away from the tone wheel on the CV shaft on 4WD, and I don't know how the 2WD arranges the speed sensors.

I dont really know where to start, and all my buddies would "cave-man" the brake sytem with a proportioning valve if it was them.

At least you know not to perform "cave-man" repairs. You'd lose the Safety Switch, and the metering/holdoff valve in that mess.

 

[Strages]

Not too familiar on how to quote off your response, but ill do my best to keep it concise.

It is a 2wd C1500
I dug this up on the web. Abs codes are more difficult to find since google just regurgitates endless engine dtc's

"Problem
Intermittent or constant amber ABS light and red brake light on. Code 61, 62 or 63 set individually or in combination.

Operation
Codes 61, 62, 63 pertain to the internal reset switches incorporated in the 4WAL EHCU. The job of these switches was to signal the ABS computer that a pressure differential is present in the channel the switch is monitoring. This ABS system is a three-channel design: RF - LF - Rears. Accordingly, there is a reset switch for each channel.

Code 61 relates to the right front, Code 62 relates to the left front and Code 63 relates to the rear wheels. The reset switch is a normally closed switch that opens with a calibrated difference in pressure against spring tension. The switch will open during an ABS stop in the pressure decrease step of the cycle to signal the computer that a pressure decrease did occur. Also, the switch or switches will open in a non-ABS stop if there is a hydraulic failure in the foundation brakes, such as a leaking wheel cylinder/caliper or air in the system."

So the codes are reset switches, 61 Right-front, 62 Left-front.

I've inspected the whole brake system, rears-fronts. Repacked the front wheel bearings, everything seems kosher.
Cleaned tone rings and wheel speed sensors and guards.
Rears looked good, in adjustment, greased some contact points, plenty of shoes and pads left on all 4 wheels.

Ive got a VSS coming as well in the near future, though the current one doesnt seem to have any issues far as i can appraise.
Parking brake switch seems to make its contact and the light glows brighter when engaged, it also fully releases like it is supposed to.

Ill look into the attached guide of yours some more once i get off work soon too.

[Cont. some hours later]
So i have fabricated the tools to depress the pistons/return valves.

The guide says i should cycle the 4WAL 6 times. Will jumping the H terminal and ground on the OBD port suffice for this step?
Is there any reason if on the the alternate method that i shouldnt use a vacuum bleeder on the unit's bleeder screws since i dont have a tool to pressure bleed via the resoviour?
Or is this a two person operation without the proper tool for the alternate method? And that i should use the two person procedure in that case?

 

[Strages]

So ive managed to make the light go away temporarily for short periods. Still persistent code 61 and 62 once they return.
I have been cycling the module using the ground and h terminal on the obd port, bleeding all 4 brakes, getting about 50mils of fluid out of each. Occasionally the fluid comes out pretty gray for the first 25mils and its pretty clear by 50mils. That was the case of the RR firstly.
Then took the truck to lock up the wheels on the dirt road nearby. A little more grey fluid from the RR and then grey fluid from the LF on the second go around.

Seems within the first two stops the pedal feels okay, but after half a minute at the traffic light at the second stop i feel myself slowly losing pedal pressure at a standstill until the brake light returns. By the time i get to the third stop i have more pedal once again during the initial "stopping". But do far as i can describe that the initial impulse seems good but i still need 75% of my pedal to finish stopping and staying stopped.
If that makes sense anyways.

I have a buddy with a tool to pressurize the resoviour and I shall try the alternate method tomorrow outlined in the pdf.

 

[Strages]

(Fixed)
So I have managed to get the light to go away, and stay away most importantly this time.

So i bit the bullet and bought some speed bleeders for all four wheels, and two additional speed bleeders that fit the hydraulic unit as well. The 8mm ones in the rear, interchange with the unit's bleeders.

What a game changer these speed bleeders are. My first experience with them.
However as a word of caution, on the cast (i think) aluminum module, threads are extremely easy to strip out. Especially i think with the type of thread sealant that comes on dorman speed bleeders isnt going to do anyone any favors.
So i had to heli coil a new set of threads into it. And i dont recommend a heli coil since breaking off the tab without marring the bleeder seat was not easy. I recommend a time sert instead, but i needed back on the road, so it worked regardless.

Anyways, bled the front and rear circuits of the module. Then bled, RR, RL, FR, then FL. Closed the 10mm internal bleeder valves on the hydraulic unit. Then jumped the H terminal and the ground to cycle the unit about 10 times and started up the truck.
The ABS light and parking brake light have both gone away, and stayed away for the last week.

 

[Schurkey]

Thanks for confirmation that grounding the "H" terminal can cycle the ABS solenoids. I don't remember reading that in any of the service manuals.