1994 burb 4WAL ABS module

[madcatter]

I've spent the last 2 days looking for something online to help and I've come up empty.

I have a '94 Suburban K2500 5.7, 235K miles. The ABS light has been on since we bought it 25K ago.

Now we're having problems with the brakes grabbing hard. It used to be VERY intermittent and only happened after a long trip down the interstate. Now they grab all the time. The pedal feels fine, there's no pulsing, I put new pads on last week, rotors are good, just checked the rears last night and everything looks good, parking brake is weak and needs the cable tightened up but that's far from a concern.

I have a reseal kit for the hydroboost since it's seaping on the damn carpet and I was considering rebuilding the master cylinder at the same time.

Now, the other half of the problem. ABS fault codes 51, 52, 81, 12, 45, 65, 67, 46, 41, 42, all dealing with valves and solenoids. My guess is bad module. Assuming that, where the hell can I get a replacement for less than the value of the truck!?!

-N8

[MT-2500]

Originally Posted by madcatter

I've spent the last 2 days looking for something online to help and I've come up empty.

I have a '94 Suburban K2500 5.7, 235K miles. The ABS light has been on since we bought it 25K ago.

Now we're having problems with the brakes grabbing hard. It used to be VERY intermittent and only happened after a long trip down the interstate. Now they grab all the time. The pedal feels fine, there's no pulsing, I put new pads on last week, rotors are good, just checked the rears last night and everything looks good, parking brake is weak and needs the cable tightened up but that's far from a concern.

I have a reseal kit for the hydroboost since it's seaping on the damn carpet and I was considering rebuilding the master cylinder at the same time.

Now, the other half of the problem. ABS fault codes 51, 52, 81, 12, 45, 65, 67, 46, 41, 42, all dealing with valves and solenoids. My guess is bad module. Assuming that, where the hell can I get a replacement for less than the value of the truck!?!

-N8

Guess at it can cost you big in the pocket book.
And still not get the repair done.
First you need to clear codes and see what comes back.
If one or 2 codes go threw the repair flow chart for the code.
If mutipal codes come back it points to power and ground and wiring problems.
I would say the brake grab is not a abs problem.
Pull fuse for abs and see what it does.
If it still grabs or act up the problem is not ABS.
Let us know what that does.
Ande what codes return after code clear.

[j cAT]

Originally Posted by madcatter

I've spent the last 2 days looking for something online to help and I've come up empty.

I have a '94 Suburban K2500 5.7, 235K miles. The ABS light has been on since we bought it 25K ago.

with the ABS light on. this model year the front speed sensors crack and then open. measure for resistance if open it is not too easy of repair.

[j cAT]

Originally Posted by madcatter

I've spent the last 2 days looking for something online to help and I've come up empty.

I have a '94 Suburban K2500 5.7, 235K miles. The ABS light has been on since we bought it 25K ago.

Now, the other half of the problem. ABS fault codes 41, 42, all dealing with valves and solenoids. My guess is bad module. Assuming that, where the hell can I get a replacement for less than the value of the truck!?!

-N8

#41/42 code is from wheel sensors left/right !

[madcatter]

OK, so I rebuilt the hydroboost last night with the basic seal kit and replaced the master cylinder with new one. O'reillys didn't have the rebuild kit in stock. No change, brakes still grab. It almost seams like the hydroboost is pushing too hard.

As for the abs, I unplugged all the connectors and killed the idiot light.

I've tried several times to clear the code using the A-H jumper "connect 2 sec.-disconnect 2 sec-repeat" procedure and got nowhere. They wouldn't clear. As soon as the jumper was reconnected the same series of codes flashed.

Tried the fuse thing too. Nothing.

And codes 41 and 42 are "Isolation/Dump Coils shorted or open-internal EBCM" in my book.

I have no idea how these two problems could be related BUT what I know for sure is: First, I've inspected/replace/rebuilt just about everyting on the service brakes and it all looks tip-top and second, I have an ABS problem, most likely in the unit/module itself.

-N8

[MT-2500]

Originally Posted by madcatter

OK, so I rebuilt the hydro boost last night with the basic seal kit and replaced the master cylinder with new one. O'reillys didn't have the rebuild kit in stock. No change, brakes still grab. It almost seams like the hydro boost is pushing too hard.

As for the abs, I unplugged all the connectors and killed the idiot light.

I've tried several times to clear the code using the A-H jumper "connect 2 sec.-disconnect 2 sec-repeat" procedure and got nowhere. They wouldn't clear. As soon as the jumper was reconnected the same series of codes flashed.

Tried the fuse thing too. Nothing.

And codes 41 and 42 are "Isolation/Dump Coils shorted or open-internal EBCM" in my book.

I have no idea how these two problems could be related BUT what I know for sure is: First, I've inspected/replace/rebuilt just about everyting on the service brakes and it all looks tip-top and second, I have an ABS problem, most likely in the unit/module itself.

-N8

The testing you have done still does not point to a ABS problem on brake grabbing.

With ABS disabled that should take them out of the picture.
With ABS disabled.
Gives us a good description of your brake grabbing?
Do all 4 wheels grab and at what speeds and at light or at normal braking or hard breaking?
Have you checked the Height sensing proportioning valve for rear wheels?
Have you done the proper bleeding on the brake system?
Is the power steering pump putting out good full pressure with brake applied and turning steering wheel?
Have you run any pressure test on the hydro boost?

[j cAT]

If the front brakes grab only I would check the rear drums for excessive wear. If the drums have more than 50,ooomi on them they usually are too worn.

what book did you use for the ABS codes ?

[madcatter]

OK, I had a chance to get the truck back from my wife for a night to check into it a little further.

I'm still treating this as 2 seperate problems.

The brake grab occurs under normal braking, at low speed. Brake pressure and height feel perfectly normal but once you get down to just a couple mph the grab and grab hard. It also does this at higher speeds if you give the pedal more pressue. If you keep it light, it comes to a full stop just fine but just a slight touch of extra foot pressure and you get a hard stop. It's as if the hydroboost is working too well, providing too much pressure.

Now, I cleared out some space in the shop and started slow rolling tests inside. It appears that the right/rear may be the cause. It's the only one leaving black marks on the floor. Everything inside the drum looks perfect but I may just buy some new shoes and springs and rebuild everything to see what happens. The left rear has a slight wheel seal leak so the shoes are damp.

Could this be a compound problem? The dry shoes on the right make them work better than the left and perhaps there's a problem with the proportioning valve allowing too much bias to the rear?

There is no height sensing proportioning valve.

The only bleeding I've done was the new master cylinder. Nothing else has been apart or leaked and the problem existed exactly the same before and after the MC replacement.

PS pressure seams fine. Brake boost is OK with the wheels turning all the way from stop to stop.

I have no pressure test equipment but it all seams fine, excessive if anything.

For ABS codes, I looked them up online and they matched what I had in the Chiltons manual.

I have a full set of OEM shop manuals on the way. I have a '90 1/2 ton, an '89 3/4 ton, and this '94 Suburban. The manuals are sure to come in handy!

What's the best resource for a replacement ABS module for this truck assuming that's the ABS issue?

-N8

[MT-2500]

Originally Posted by madcatter

OK, I had a chance to get the truck back from my wife for a night to check into it a little further.

I'm still treating this as 2 seperate problems.

The brake grab occurs under normal braking, at low speed. Brake pressure and height feel perfectly normal but once you get down to just a couple mph the grab and grab hard. It also does this at higher speeds if you give the pedal more pressue. If you keep it light, it comes to a full stop just fine but just a slight touch of extra foot pressure and you get a hard stop. It's as if the hydroboost is working too well, providing too much pressure.

Now, I cleared out some space in the shop and started slow rolling tests inside. It appears that the right/rear may be the cause. It's the only one leaving black marks on the floor. Everything inside the drum looks perfect but I may just buy some new shoes and springs and rebuild everything to see what happens. The left rear has a slight wheel seal leak so the shoes are damp.

Could this be a compound problem? The dry shoes on the right make them work better than the left and perhaps there's a problem with the proportioning valve allowing too much bias to the rear?

There is no height sensing proportioning valve.

The only bleeding I've done was the new master cylinder. Nothing else has been apart or leaked and the problem existed exactly the same before and after the MC replacement.

PS pressure seams fine. Brake boost is OK with the wheels turning all the way from stop to stop.

I have no pressure test equipment but it all seams fine, excessive if anything.

For ABS codes, I looked them up online and they matched what I had in the Chiltons manual.

I have a full set of OEM shop manuals on the way. I have a '90 1/2 ton, an '89 3/4 ton, and this '94 Suburban. The manuals are sure to come in handy!

What's the best resource for a replacement ABS module for this truck assuming that's the ABS issue?

-N8

Have you disabled the abs brakes and see what it does with the disabled?

[madcatter]

I unplugged everything to the ABS unit. That took care of the idiot light no change otherwise.

-N8

[MT-2500]

Originally Posted by madcatter

I unplugged everything to the ABS unit. That took care of the idiot light no change otherwise.

-N

OK
You have a regular hydraulic brake problem or brake lining problem.
In would also do a complete brake bleed abs and all 4 wheels.
Check brake adjustment and calipers and brake hoses and rear wheel cylinders.

[madcatter]

I'm going to rebuild the rears. Shoes, springs, cylinders and wheel seals and see what I have after that.

I have the dealer manuals now and came up with something else. It says if you have these solenoid codes and the codes won't clear, replace the BPMV. According to the book, there's no alternative.

SO, I guess it's a trip to the salvage yard for the whole assembly. Some day. I'm not paying what the truck is worth to repair the ABS. Basic brakes only for now.

Any other suggestions on where to get this thing?

-N8

[madcatter]

So I replaced the rear wheel seals, wheel cylinders, shoes, spring kits and adjusters. I still couldn't find anything wrong but something fixed the problem. The brakes work perfectly now.

Back to the ABS issue, I have a 93 S10 Blazer I'm parting out for a project truck and it has the 4WAL ABS as well. Is the module and BPMV interchangeable with the Suburban? They appear to be exactly the same.

-N8