RWAL ABS & e-brake lights-on... chronic condition
 

I've been living with these two warning-lights, for years, but recently noticed the rear wheels locking up quite easily - something I'm pretty sure is new - so I got back into trying to diagnose/fix the problem.

Following FSM, I switched on the ign and shorted pin 13 of the DTC to ground. ABS warning light began to pulse. Fault code was 7, assuming I'm understanding the interpretation correctly, and 8 if not...but either way, I followed the diagnostics.

For "7", it's: "Electronic control module [CAB] fuse pellet open, isolation output missing, or valve wiring shorted to ground." (For "8", it's identical, but also casts suspicion on the other of the two RWAL solenoids, which tested OK, too.)

More detailed FSM troubleshooting instructions note the following possibilities:
"Short to ground from terminal 1 in the 14-way connector to the RWAL valve." (by which they've GOTTA mean the CAB connector, since the RWAL connector is only a 4-pin deal). Tested - found no short present.
"Short in the RWAL valve's isolation solenoid." (SB 3-6 ohms). It tested within range, and solenoid will audibly click when hot-wired.
"CAB." OK, I will deal with that, then.

So I found a "guaranteed" used CAB on ebay, ordered and installed it, and...you guessed it, lights stay on. The DTC is supposed to reset when the CAB is disconnected, which of course I'd had to do to replace the original anyway, but the same or similar (7 or 8) fault-code continues to display.

(I found no "fuse pellet" during a close inspection of my old CAB PC board - it's easy to open up the plastic housing - and the rebuilders indicated they were not aware of such an animal either...only wish I HAD, since it would at least be something to point at, if not replace.)

I've tried other stuff that isn't really indicated in the DTC to fix this, eg replaced the speed-sensor, replaced the MC (pedal-sinking was alarming - I guess I'd lost one brake circuit) but like I say, if I'm going to believe anything in the FSM, I should have faith in the accuracy of the codes...right?

All I can think to do at this point is to see if I can find an actual rebuilt CAB that's at least less likely to be internally flawed than my ebay purchase, but it now seems to me like that's inevitably going to be just an expensive disappointment.

Anyone?

Mahalo - Dave

That was my symptoms when the brake light switch went on me.
The switch has about 6 sets of contacts and if they don't make contact the brain thinks the pedal is stuck or some other problem and lights go on, It also disables the ABS system so when the back tires want to break loose there is nothing to prevent it.

AYFKM?? ;)

I will definitely check that. It's hard to believe that the FSM would skip that as a possible cause.

I just looked at the FSM "stop lamp switch" schematics (appears in two or more locations depending on coverage), and yes, there are three sets of contacts, so six terminals, with just one set of contacts devoted to the CAB input...sounds just goofball enough to be the perfect fix. If I get continuity between terminals 1/2 while switch is in place & there's no pedal action, that's a problem - hopefully THE problem.

Future ref - dug from schematics:
terminals 1/2 (N.C.) are CAB-sensing pair, normally grounded via 2, and isolated when pedal down
terminals 3/4 (N.C.) form one set, open on braking, to interrupt cruise-control
terminals 5/6 (N.O.) are the stop-lamp-switching pair

I'll post back after weather improves and I've had a chance to check this...

I forget exactly how the 3 sets of contacts work but basically there is one set for the brake lights, one set to disengage the cruise and the last set to ensure that the brake pedal is NOT depressed when the cruise is engaged, so I don't remember if you get the same reaction from all three sets when the pedal is operated. I must be sleeping or something... I see you have already found the contacts and which are Normally open and which are normally closed, should be able to pin point from that info. The brakes switches are very poorly made and have been a known problem for many years.

nothing to see here....
 

Well, my hopes were dashed; the switch is out on my desk now and tested fine, though yeah, I suppose it could be an intermittent problem, like oxide-crap in the switch that... what, somehow keeps contacts closed when the pedal is down...but...I kinda think replacing it would be good money after bad. (I could see dirt keeping contacts from CLOSING dependably, but not so much from opening that circuit.)

I ran across yet another reference in the FSM to a fuse within the CAB - not that it'd normally be user-serviceable - but I'd like to know if it's there, because if I could find it, it would at least be a smoking-gun, and I'd either ghetto-repair it or feel better about shelling out the $$ for a replacement. No PCB components jump out as being different and therefore likely to be a fuse, "pellet fuse," etc. Anyone?

"A fuse internal to the CAB, provides a fail-safe
device which prevents unwanted control over the isolation
and dump solenoids. The fuse is in series with
the isolation and dump solenoids output circuits. If
the internal fuse is open, the CAB cannot provide
voltage to energize either solenoid and antilock stops
are prevented. I f the fuse is open, the braking system
will operate normally but without antilock control
over rear brake pressure."

Due to the long history of these switches I would change it out on spec, they used to be less than $20.

I used to work on these at the dealer. Have you verified the fuses including those for trailer wiring are good? I always verified with a DMM (or Power Probe) as visual would not always show a bad fuse.

FWIW, the brake switch can be misadjusted and still function for brake lights but still turn on the ABS light.............. Ask me how I know.

Readjust it, it is free and will confirm that it is not the issue.

Pat, I hope you're my savior yet again.

I was thinking along just those lines when I reinstalled the stop-lamp switch, hurriedly, to head out last evening. I didn't have time then to go re-read or print what's in the FSM on 'adjustment,' but now that I've re-read it, almost none of the key parts make sense:

"STOP LAMP SWITCH
(1) Push and hold brake pedal down
(2) Pull switch plunger all the way out to fully
extended position.
(3) Push switch plunger Inward 4 detent positions
(or clicks). This is required preset position. Plunger
will extend approximately 14 mm (0.55 in.) out of
housing at this setting.
(4) Release brake pedal. Then lightly pull pedal
fully rearward. Pedal will adjust switch plunger to
correct position as pedal is moved to rear.
CAUTION: Do not use excessive force to move the
pedal rearward for switch adjustment. Excessive
force will damage the switch."

but..."Pulling the plunger out" is...what the switch's internal spring does, no?
um, "detent positions?" and four of them? that are intended to be 'felt' when one presses the plunger? I've got no clue what they're on about with that - mine surely doesn't work that way. If that sentence were not so clearly written, I'd think they were talking about a whole-switch-mounting setup that has four detent positions (again, not what *I* have, as far as I could tell)

I did notice that there's an extremely slight "unused pedal return" range, so to speak - I can pull it up towards driver very slightly. Whether that's enough to make the difference in the 1/2 contacts being kept open is another question. Anyway, ignoring the FSM instructions above about adjustment, I noticed there are a couple of maybe-5/16"-hex-head screws that looked like they clamp down through a slotted bracket on which the whole switch rides -- now THAT would have been my guess as to the real means of switch adjustment. Is that it?

But before I go stabbing off into the darkness again, I was thinking I'd test the contacts in situ to see if that's really keeping the ABS contacts open, even with the pedal relaxed/up...but then realized by the time I got done with that I'd be in a cervical collar. But happily, the FSM shows that the ABS contact in that switch leads up to pin 7 in the CAB connector, which would be much easier to test from. So if pin 7 is grounded while the pedal is relaxed, well...it's my huckleberry...

I tested as I'd described above - for continuity to ground from pin 7 of the CAB connector (white/pink). And dammit, it performed exactly as it should (no pedal = switch closed/ground connected to CAB), testing consistently for ten or twenty cycles, so I will leave the mystery of proper stop-lamp-switch adjustment to some future date.

Also tested all fuses in the compartment, verifying that 12V is getting through them. One ckt failed (a 5A fuse for "illum") in that there appears to be no feed to it - but FSM shows it having to do with panel-illumination, which isn't even a problem AFAIK, so that's nothing.

If it matters, the ABS/brake warnings come on immediately on key-on, only going out during key-over to start, then immediately on again.

Anything else? A rebuilt CAB, and... maybe continued problems?

LOL, I have never adjusted them like the FSM says. I just reach under, twist it out, pull the plunger out a click or two, and shove it back in and twist to lock.

Never failed me yet.

That being said, you don't have a brake switch issue, because the light does not come on immediately, rather they come on after you have reached around 20 MPH.

I would put a new 5A fuse in that circuit anyway, you never know when one part of a circuit interacts with another........

Thanks, Pat.

I got all my eggs in the "new CAB" basket.

Failing that, when you see a beaten white '97 dually fishtailing and getting sideways while braking hard, think of me...

New year, old problems.
 

Filling in the one or two heartbreaking chapters I didn't write in the last few months, I've replaced the CAB with a new (rebuilt), and as of today, replaced the hydroboost. Same-same. ABS & brake-lights remain on. I'd suspect broken-wires-in-diff-speed-sensor-plug (and will check this when I get my dump-bed operable again) but the fact that the lights come on before I've even moved the truck don't jibe with it being a speed-sensing fault...right?

I wouldn't be doing all of this just because of the warning lights; for the last 3 days it's felt like no power to brakes (but no problem with steering) and I've had a chronic hydroboost drip that just needed to get fixed before any more rubber beneath it gets dissolved, so the hydroboost seemed like a likely candidate.

Now I've got the power-brakes back, but I'm also back into the "OPPOSITE of RWAL," wherein it's almost impossible to stop, at least from low-speed test-driving, WITHOUT my rear wheels (all four - it's a dually) skidding audibly.

Previously, I changed the MC and diff speed sensor, and as I mentioned above I just replaced the hydroboost today. Now I'm turning my gaze on the combination valve, because, well, the rear wheels are locking up most of the time right now (and this thing is supposed to proportion, right?) and because it's maybe the 2nd-to-last item that I have NOT replaced yet (I've not touched the RWAL valve - I think the last item possible - because last I checked they just weren't available anymore, and because the solenoids work...neither of which means it's any good, I suppose). I couldn't do a worse job of shotgunning if I'd just ordered all new brake components years ago when this problem originally cropped up.

If I take the proportioning/combo valve out, is there anything to "look for" to indicate it's been misbehaving?

Trouble-codes said that it was the CAB - probably still do. (yeah, thanks, trouble-codes...)

I did a little reading in the 2000 factory manual and I know yours is a 1997 and may be different. It says that the codes do NOT reset by disconnecting the batteries and must be reset using the DRB scan tool or 50 restarts. It also says that if the CAB is replaced the tire size and revolutions per mile must be programmed in using the method in the chassis diagnostics manual. It also says that the brakes must be bled then an anti skid test done to cycle the valves then the brakes bled again. Also on 2500 and 3500 the brake proportioning valve is eliminated and an "electronic brake distribution" EDB is built into the ABS to control the rear brakes. The EBD will not work if the brake switch is not closed, (brake pedal depressed), the red brake warning light is on, vehicle is in 4X4, an ABS system fault critical to EDB, or more than 2 ABS system faults are present. With all this in mind the red light can also be put on by the parking brake switch either from pedal droop or out of adjustment.

Jeez, if I had a 2000/ 3rd gen, I'd be asking you to just shoot me now. But yeah, pretty sure those hoops didn't exist for 1997-vintage models, though later today I'll (again) review the FSM to see what I can see. I've been up and down the FSM brake sections repeatedly (though not recently) so I'm pretty sure that stuff would have registered in my ailing memory.

I did make the silly mistake of overlooking the brake-switch height resetting yesterday when I replaced the hydroboost - discovered the glow of always-on brake lights last night - but also not expecting that to change my warning-light situation, since the ABS light comes on before the vehicle is even set in motion (during which time it would be entirely reasonable to have one's foot on the brakes).

From some other threads, I do want to get back into the harness between diff-sensor and the next connector (wherever that is) and verify continuity. Seems at least a few people have reported open circuits there, from wire broken within insulation near the sensor at the diff, I think.

The reason I mention the differences in the model years is because of the replacement CAB you got, perhaps it was the wrong one. Also don't rule out the parking brake switch as it also puts on the red light. Also if the wires to the rear diff sensor are damaged and need to be replaced don't forget they are a "twisted pair" and not just any wire. One other thought after reading the thread again, are you using a digital multi meter as they "sample" and it's possible to miss an intermittent fault.

Very good point, regarding these brake light switches. I have seen cases (not for this specific problem) where the contacts just get a bit of resistance between them that can cause troubles like this. This resistance can often be intermittent, and can be dependent on the amount of current passing through the contacts at the time. Just be careful of ruling out that switch too quickly.

Thanks, guys.
- new CAB has same p/n on it as my original, and as the junkyard one I bought, so I doubt there's any problem there
- brake-light switch was definitely misadjusted via my replacement of the hydroboost, but once I refreshed my memory of how it's supposed to be reset (simply one-minute procedure) the brake-lights returned to normal status
- I was briefly excited when I found no (audible) continuity between pins 13 & 14 at the CAB connector (that's the twisted-pair that heads back to the sensor in the diff), for some reason having jumped to the conclusion that I should be seeing something like zero ohms. I even bypassed an unnecessary inline connector set because shorting through the pair just ahead of them gave me the continuity "beep," but then of course once I'd spliced the cut ends back together, there was STILL no audible signal...that's when I realized no one had told me it was a near-zero resistance. I'm getting 1900 ohms, seeing that some others have reported 1300 ohms, and I suspect there's a broad range of passing resistance values. I'll dig out my old spares (it's been replaced at least twice) and see what those meter, but I think that's another wrong tree.)

Oh, and though my DVM does have a couple of memory options, I almost never use them so as to see the dynamics in any reading.

To be thorough, I do need to recheck for continuity/open on stop-switch terminals 1/2, which (going back in this post) should have pin 1 grounded via pin 2 normally (with pedal at rest), and with pedal pressed, that pair is supposed to be open, telling the CAB that the brakes are on, so it better start looking for any wheel-slippage. This worked flawlessly when I tested it before - and I tested it many times then - so I don't see this being a new problem or a metering failure.

I do owe myself another bleeding session (front-brake reservoir dropped rather fast, and it doesn't help that I back up an insanely-steep driveway daily, which spills that fluid forward into the rear-brake reservoir IIRC).

But failing alla that...swap out the proportioning-valve? Then yank out the ABS valve and see what I can see with it on a bench? I dunno what's in it - any orifices to clog? There were times when the fluid in my old MCs was really nasty-looking - no idea why - and I figure that gunk accumulates worse in some low-point in the system, maybe even after many bleeding sessions.

Thing with the proportioning-valve is that the only electrical communication it has with the rest of the system is that one "grounded-when-bad" switch. And that's always tested as un-grounded. So although the valve might screw up at times and explain my grabby rear brakes (sometimes), it can't convincingly explain my forever-on ABS light. The grabby rear brakes are actually relatively recent, like...the last six months. The ABS light has been on for more like a decade.

Mine was similar and it was the light switch. There are 4 or 5 different sets of contacts in that switch and it is quirky in its set up. If the plunger is set up wrong some of the contacts can still be open, not necessarily the ones that light up the tail lights. Then the system thinks there is a problem and shuts down the ABS. With an empty bed that means rear wheel lock up when you even think about stopping.
I fiddled with the old switch for days then just gave in and bought a new one. DO NOT PULL THE SHIPPING PIN BEFORE YOU HAVE IT INSTALLED.
Once you get the switch in make sure the pedal is up in it's resting position THEN pull the pin. The plunger will pop out until it touches the pedal and that sets up the switch.

VADSLRAM - OK, I give...got a switch on order. It's $10. Guess I could crowdsource for that...seriously, though, it's nothing in my spectrum of costs in time and dollars spent on this, though I have about a half-percent hope it will make a difference, since the contacts all checked out OK.
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I tested wheel speed-sensor output conclusively (I believe): pins 13 & 14 at the CAB connector give me an 1800ohm reading, and today I drove with my meter (AC volts) connected to the same pins. It varies smoothly from zero V to around 16V at 60MPH. I can't see that being a problem. I also can't find any specific testing data in the FSM; they just describe connecting it to do testing at the factory, on a set of rollers, but it's just not going to fail in a way that I get some "wrong" voltage out of it.

Looking further to the proportioning-valve, the FSM says this:
Is that "stem" accessed/ probed with a tiny screwdriver or dowel, if I pop off the rubber cap at front of the valve and put the dowel into the hole there? If that checks out, I'm inclined to skip messing with that component and go directly to the ABS valve, where unknown peril lurks.

the long nightmare is over.
 

I'm happy to report that I've got brakes like never before (I think literally since I bought the truck) and almost as importantly: no freaking RWAL/brake warning-lights!

UN-satisfyingly, though, I can't point to any one clear smoking-gun, in the end.

Installing a new hydroboost: this left me with same warning-light conditions, but while changing it, I'd been noticing that when on the steep hill where I have to work on it (I know, I know - great place for brake work), the MC reservoir for the front brakes was dangerously low due to the inclination, and the fact that the port into the MC itself was on the higher end. It's conceivable that it managed to suck in some air there, and I'd not re-bled the brakes for a few months...and I still didn't, because I just didn't really believe that could have happened.

Next, I did some other electrical testing, confirming things like the brake-pedal switch were operating as expected.

I moved on to the diff speed sensor (again.) Here's where my diagnostics went out of round; I for some reason had been thinking the speed-sensor would appropriately be "beep-tested" for continuity, meaning a very low resistance would give me a "beep" from my DVM, and I'd be able to work through the wiring checking for continuity without having to keep my eyes on the meter in the cab. So when that test gave me no beep, but shorting through the insulation across the sensor leads just cabward of the last plug DID, I jumped to the conclusion that, as some others had reported, I'd lost continuity (broken wire) in the last few inches of harness before the plug. So I cut out that redundant plug/jack and solder-spliced the wires there...and then was greeted with STILL NO continuity-beep from my meter.

It was only then that I began to question my assumption that the sensor resistance should be nearly zero, and googled to find that actually, there should be about 1800 ohms of resistance across the sensor.

So did I fix anything there? Well, not according to the warning-lights, which stayed on.

When I next got into it, I was heading towards replacing the proportioning-valve, since the symptoms lately had been as if the brakes were biased heavily to the rears. I posted to ask precisely how to test the proportioning-valve per the incomplete instructions in the FSM, using a dowel or whatever, but didn't get a reply. While test-driving after the hydro-boost, I could hardly help but lock up the rear end - it was insane.

So before replacing it, I owed it to myself to re-bleed. Having replaced my bleed-ports with those aftermarket check-valve types, it's a bit easier, too.

This would be far from the first time I'd tried to bleed my way out of the problem, but given the low-reservoir condition, and the mysterious dirty-looking fine debris that keeps accumulating in my reservoirs, I figured it was warranted again.

I couldn't position myself to be able to see if/how much air was coming through during bleeding, but when I was done, I held my breath and keyed over. The ABS light self-tested and went out, as often. It came back on immediately after I started...but then went out, as did the red e-brake warning light! I've not seen either light misbehaving since, which really amazes me, since I think this has been going on since about a year after I bought the truck, around 2005!

-----
If there's anything to complain about now in the realm of my brakes, it's that they're 'sticky.' When I took my wife out the other day, having released the e-brake and then barely teasing the beast to get in motion down our insane-steep driveway, it was like the brakes were 'stuck on.' And they released with a jerk that made my wife gasp, giving me that look...

The stickiness also appears from time to time while driving, especially when coming to a complete stop with foot on brakes: it requires a whole new level of finesse, so as not to get that minor whiplash sense that novice drivers go through when learning how to brake smoothly to a stop.

But hey - I have SERIOUS brakes now, better than ever, so I'm not complaining, at least not very loudly. I'll have a spare brake-light switch when it comes in, too...and probably a spare speed-sensor or two if I look around in my junk hard enough.

Thanks all for the contributions to my Decade of Diagnosis.

Dave

Glad you got it working. Your last post got me thinking, your steep driveway may have had a lot to do with your difficulty in successful bleeding. The air likes to rise to the top, and if the incline was making your bleeders that much lower than the master, it may very well have allowed a difficult bubble of air to have been trapped somewhere. I have experienced a difficult bleeding job or two, where raising the rear end of the vehicle on the hoist, to almost vertical, was necessary in getting the last bit of air out of the system. Just a thought.

Same problem, but - locking rear wheels was caused by leaking axle seals greasing the brake shoes and drums. I feel your pain. It's tempting to tape over the warning lights and forget them.

I had some vehicles with that "stickiness" on brake release you describe, and found that in some cases going to DOT 4 .SL6 brake fluid cured the problem.
.SL6 has about half the viscosity at cold temps than standard DOT3 or DOT4.
It is mainly used for vehicles with electronic stability control where quick filling of the pumps is important.
It is compatible and mixable with DOT3 and DOT4.

HTH

Markus

Sigh. I prolly have that going on, too. Any visible evidence outside the drums, eg oozing oily stuff? My working facilities suck in the extreme, so even the notion of jacking it up (on a dirt slope that's only occasionally not soft & muddy) don't support my mechanical interest in getting eyes on it.

I actually swapped over to DOT 4 a couple of years back, not on any really sound basis, just the sense that it might be of higher quality and less hygroscopic than DOT 3. I don't think I really did my homework on that, though - something I'd picked up from a pre-internet-age buddy, so it might or might not be true. (I definitely didn't do it to winterize my truck, here in Honolulu...)

Well, in the cases where .SL6 spec did help it was because the fluid would get out of the brake cylinders quicker when releasing the brake.

Since you will have a bit of salt in the air, maybe you should check your calipers and the mechanics inside your drums for rust that makes them sticky.

Sometimes the front brake hoses degrade on the inside and swell shut, also delaying the release of the brakes.

That was so long ago I don't remember if there were external signs. It seems that the brakes grabbing created suspicion so I opened things up to look. It doesn't take much oily stuff on the shoes to cause the brakes to grab.