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Rear ABS Illuminates -- will not produce fault code at test

Kaajot

Micro Machine Manager
Hello-

I've checked multiple sources, videos, searches and have a good enough understanding on how to check my ABS when Rear ABS illuminates. The Brake light is not illuminating, reservoir is full. I replaced the Speed Sensor at the rear axle last August to fix up its fault code. No fault code for it now.

However, if I'm driving and get about 40-45 mph, maybe 35 mph occasionally, the Rear ABS light illuminates solid and does not go out. The truck feels like a boat and is very unstable in this as well. Now I know I need to do my right tie rod (have a new one, just waiting to get a non-bent rim for that tire and to do it all at once), but that pull was evident months ago and now the Rear ABS is causing a whole different danger zone of slop (I do not drive fast nor far with the truck at this point yet again).

Here's the kicker. I have tried to pull the code 2 through 16 by grounding (after key on) the ABS II style tester. It's under the glove box, and supposedly it's supposed to have memory too if it's the ABS II. I've tried every grounding to steel, negative battery ground and direct to negative battery. I cleaned the ABS II pin and tried going behind just in case to make better contact with the wire, but I'm not able to get codes for the Rear ABS Fault. I drove and triggered the fault, kept the engine running, and tried grounding the tester and still no code just in case it was acting like an ABS I and would wipe the codes upon power off to the truck.

Any ideas? I feel like it could be my Speed Sensor went bad, but I should be getting a computer code too. Since I get a fault triggered but I cannot get the fault code, I'm leaning towards the Rear ABS Module behind the glove box being bad? I mean, it's 27-28 years old so.... maybe?

Anyone ever had a problem pulling the Rear ABS fault code test? Solutions? Common causes?

Thanks.

-KJ
 

Kaajot

Micro Machine Manager

Fellro

Moderator
Staff member
You shouldn't notice any difference in how it drives just becasue the ABS is out, it only pulses the the brake to prevent brake lockup. It does not apply pressure when you don't. I actually only backs off the pressure, not apply. Basically, when ABS is non-functional, your brakes will behave as normal. One thing I have found before is that the physical abs control can fail and will actually block pressure from getting to the rear brakes. On that truck I just removed the entire ABS system. We also are not subject to safety insppections, but there are times the vehicle will be safer without the damn ABS.
 

Kaajot

Micro Machine Manager
You shouldn't notice any difference in how it drives just becasue the ABS is out, it only pulses the the brake to prevent brake lockup. It does not apply pressure when you don't. I actually only backs off the pressure, not apply. Basically, when ABS is non-functional, your brakes will behave as normal. One thing I have found before is that the physical abs control can fail and will actually block pressure from getting to the rear brakes. On that truck I just removed the entire ABS system. We also are not subject to safety insppections, but there are times the vehicle will be safer without the damn ABS.

So, I know my right-pull when hitting an abnormality in the road was my tie rod, which is evidence from the front right wearing down despite replacing the tie rod 2-3 times (and drag links and bearings etc etc) because the Rim is likely bent/warped, and I'm going to get a new rim, new set of front ties, and then fix all of it.

But why when the R ABS light came on did my driving go to crap? I know my braking seems slower, but no visible leaks or loss of brake fluid. It feels very much like a boat right now since the light came on.

I guess the worst thing I can do is continue pulling the module out to get its number and see how it runs? Will removing the module short the system into default driving, or is there more to it to elmination?

MI Plates on the truck so no inspections but if I put NYS plates it'll be a problem (I think I only get out of emissions part of the test due to age of truck).
 

Fellro

Moderator
Staff member
Might simply unplug the module and see, otherwise check for brake drag. I suppose it could be possible to have the brakes holding pressure with a failed actuator. Kind of like when a brake hose fails internally and holds pressure.
 

Blue-Truck-Nut97

crank polisher
551
18
You shouldn't notice any difference in how it drives just becasue the ABS is out, it only pulses the the brake to prevent brake lockup. It does not apply pressure when you don't. I actually only backs off the pressure, not apply. Basically, when ABS is non-functional, your brakes will behave as normal. One thing I have found before is that the physical abs control can fail and will actually block pressure from getting to the rear brakes. On that truck I just removed the entire ABS system. We also are not subject to safety insppections, but there are times the vehicle will be safer without the damn ABS.
Just adding to your statement here, if it blocked pressure to the rears, thus doing all the stopping with the front, combined with loose steering, bad tie rods, bent wheel and who knows what else at this point, sure could account for bad handling in my opinion.

Sent from my E6810 using Tapatalk
 

Kaajot

Micro Machine Manager
Just adding to your statement here, if it blocked pressure to the rears, thus doing all the stopping with the front, combined with loose steering, bad tie rods, bent wheel and who knows what else at this point, sure could account for bad handling in my opinion.

Sent from my E6810 using Tapatalk

Yeah, what you and Fellro makes sense. The back differential and drums were rebuilt ~4.5 years ago. New lines, so that's why they're not busted, but maybe something is blocked back there.

I'm getting to the module first thing in the morning tomorrow, soldering in a new pig tail to the distributor (finally) and then servicing one more generator and my spare lawn mower. (Got 2 Champion Generators, Weed Whipper, and Mower serviced plus flag pole rebuilt and up and repainted and the new Saab wheels Chromed and mounted finally, so moving along here). Truck's about to get some attention and then when DMV/SOS opens up F-150 will go in for that engine servicing -- towing 1K gallons of water to the farm so I can manage the animals while it's getting diagnostics and hopefully that head job done.

Oh, one other thing -- I threw a new Neutral Safety Switch in last month and unfortunately fixing the pins may have bungled up the reverse lights sensor AND it's now actually requiring a little jockeying to start -- think I have the alignment off, but also know I stripped frayed the pins trying to add a new terminal cap, gave up and put the old one back on. Unsure if the NSS wiring communicates much with the ABS module -- I do know it is infact responsible for my reverse lights not firing unless I jockey the driving switch between Reverse and Park and lift up just a little to make the contact realize I'm in Reverse and need those lights on.

That's on my radar but again, I don't think it's the main factor in the Rear ABS going very off. It does feel like there's some drag once the light illuminates and it does feel like the front brakes are doing most of the work -- I think they have for awhile actually. I'm going to guess it's a bad module (will find out, probably a fried capacitor or burnt trans path) and the blocked rear pressure.
 
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Fellro

Moderator
Staff member
If it is blocked, and related to the abs, it will be the actuator that is located below the master cylinder on the frame up front. I removed that on the 92 when it was only working the front brakes. Bad deal on a truck that regularly tows in excess of 10,000 pounds.

https://www.rockauto.com/info/1/122024-rit__ra_p.jpg
122024-rit__ra_p.jpg
 
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Kaajot

Micro Machine Manager
If it is blocked, and related to the abs, it will be the actuator that is located below the master cylinder on the frame up front. I removed that on the 92 when it was only working the front brakes. Bad deal on a truck that regularly tows in excess of 10,000 pounds.

https://www.rockauto.com/info/1/122024-rit__ra_p.jpg
122024-rit__ra_p.jpg

Found it for my unit too -- should be easy enough. Will I have to bleed brakes? I've got a manual, if the process is there I can read it.

Did you eliminate it though? Or upgrade?

I don't do 10K lb loads often (once maybe?) but 2K - 6K is not infrequent, every few months. I've already upgraded the Suspension to F250 in the back, springs, etc. Some day I plan on upgrading the front controls to F250/350 bearings to accept that kind of work more regularly. The Spring Coils up there are already upgraded, but I think I run through wheel bearings too fast due to the loads I exceed (legally, way beyond GVW, etc). Although the more I think about it, the more I think the blockage may have been in the back for a long time. I've been wearing through my front brakes, calipers, rotors, etc everything up front way too often and my former mechanic (he's out of business) never thought much of it.... so, maybe this ABS thing really is the fundamental problem to my way-too-frequent bearings, tie rods, etc that I've replaced since 2015.

The first 6 years they were fine, then transmission blew and well, too many fires on one vehicle and I think not enough SA by mechanics to really get a grasp of all the problems at once.






Not Related: Forgot, when I did the Neutral Safety Switch swap to a 1995 upgrade (better rain seal to keep moisture out) I also redid the wiring from the amp to the starter solenoid. New, heavy duty inline fuse and beautiful wiring done properly and housed securely out of the way of heat and oil. That fixed some more of my alternator fluctuations and now it's just needing some tweaks to the tensioner and power steering pump to likely keep the belt from any slipping that causes erratic amp fluctuations when turning slowly in low gear. No overcharging of battery or anything else and the amp stopped failing again, so the wiring was a big step in the right direction of getting rid of grounding and shorting issues on that power line.
 

Fellro

Moderator
Staff member
I simply removed and bypassed the actuator. Yes, you have to bleed out the rear brakes no matter whether you replace or bypass the actuator. The F350 it was on tows big round hay bales, horse trailers, and other such things regularly.

Regarding the NSS, I do agree it seems out of adjustment.
 
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Kaajot

Micro Machine Manager
I simply removed and bypassed the actuator. Yes, you have to bleed out the rear brakes no matter whether you replace or bypass the actuator. The F350 it was on tows big round hay bales, horse trailers, and other such things regularly.


TL:DR -- Where the heck is the ABS Hydraulic Control Unit and how can I tell if it's been bypassed/eliminated if I am indeed looking in the right places and it's not there? (PS it's a 1992 F-150 Custom, so a 1991 bodystyle and some components possibly, if that helps. Also has the ABS II location for ABS Control Module).

Have been limping along on this issue. A lot going on, but that's life.

Anyway, had to repair the tail gate handle -- snapped off on me July 2, so finally got a new one and put it in. Oiled all the moving parts, probably going to find some grease for the tailgate ends later (only had some used oil from small engine maintenance) so they stay less-resistant and don't stress the tailgate handle lift to fracture on one side and put me through this exercise again. I think last time I repaired this (2 years ago?) maybe it only received lithium or worse, w-d40, and didn't stand through the weather obviously. Definitely needs a thick grease.

After that, I went crawling around looking for the ABS Hydraulic control unit you linked to, I've found (going to buy on Amazon, best deal) and cannot for the life of me find it. I've read this could be eliminated, as you mentioned, but is not what I want to do.

I watched a YouTube vid of a guy working on his 94 or so and the control unit looks like it's underneath the truck, not below the brake master cylinder. Either way, I've looked at both spots and do not see this control valve for the life of me. What kind of evidence would show it had been eliminated by the original owner before me? Or there's a chance a very unscrupulous mechanic eliminated and made it sound like a good idea also when he repaired the back brake lines. I don't recall and won't be asking him as he has a court ordered judgment and still has not paid me a cent. But I definitely am not seeing the abs hydraulic control unit -- it could just be my eyes though missing it. I've lots of references of the part (in this thread, on rock auto, on amazon, on ebay) so I know what it looks like but just do not see it in any of the places I'm expecting to find it.

If I can find it on the truck, I'm ordering a new one. I reason even though my abs module is bad and won't show faults, the control unit is not working properly and I think I can hear the spring inside it on occasion pop from a compressed position. And my truck drives like it has some major drag in the bag, so I think the unit is sending bad signals to compress or whatever causes it to give more tension to the rear brakes.
 
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Kaajot

Micro Machine Manager
Anyone know where I can find the ABS Hydraulic Control Unit on a 1992 F-150 Custom 4.9L, or what would be a tell-tale sign that it has been deleted/bypassed?

Orrr, is there a way to have an ABS I or II system and not have one of these installed?

Thanks, not a lot of information on my exact situation on other forums or videos. It's generally either there or it's a video bypassing it, but I don't really see any evidence (or know where to find the evidence) that it maybe was bypassed.
 

Fellro

Moderator
Staff member
Trace the brake line from the master down to the frame. Inside the frame channel will be where it is mounted, just a bit rearward of the firewall. (I checked my 88, it was right by the fuel filter) You must have an actuator for the ABS system to function. It's primary function is to pulse the brake pressure so that it is not a continuous hold so they can still turn rather than lock up. It is only done hydraulically. In essence, you jam on the brakes and it backs off the pressure a bit to allow the wheel to turn and the pads to engage a little lighter than you are actually requesting. You can do the same thing by "pumping" the brake as you would in slick conditions. It just does it faster and without you having to think to do so.
 
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Kaajot

Micro Machine Manager
Trace the brake line from the master down to the frame. Inside the frame channel will be where it is mounted, just a bit rearward of the firewall. (I checked my 88, it was right by the fuel filter) You must have an actuator for the ABS system to function. It's primary function is to pulse the brake pressure so that it is not a continuous hold so they can still turn rather than lock up. It is only done hydraulically. In essence, you jam on the brakes and it backs off the pressure a bit to allow the wheel to turn and the pads to engage a little lighter than you are actually requesting. You can do the same thing by "pumping" the brake as you would in slick conditions. It just does it faster and without you having to think to do so.

Oh man!

I'm going there right now. I literally did not look right behind the firewall, but I sure as heck know the fuel filter location and know I didn't look in that cavity area.

BRB!

Holy mother of sweet baby jeebus, I'll be a monkeys uncle yeah about 3' forward of the fuel filter rail the last rusty part I got is clearly an ABS Control Unit.

Ordering on Amazon. It prices out about $50 cheaper with farm tax exempt and a rebate going on for the core exchange right now than even Rock Auto.

THANKS! I'll take pictures of the rusty one and new one in daylight when I get to work on it. I'd rather change this part out first (as you said something is causing the ABS light to illuminate) before I buy a new ABS Control Module. Maybe I'll be able to pull codes once it's swapped... there was a lot of oil under this truck a year ago and I keep finding myself repairing the wiring because of it, so possibly this wiring bundle is the cause of the module not communicating in diagnostic....

Thoughts on that idea regarding the diagnostic not working?

But definitely with no leaks anywhere and a full master cylinder, this OEM 25+ yr component is a good change even if it's not the actual culptrit.

Funny thing, my old buddy/mechanic Keith has sworn a thousand times my truck doesn't have ABS, but I always tell him the ABS light does work (has in the past). And after finding the control module I found it pretty dumb if they put a module in the truck without an actual system to control. Sooooo happy I know where this is now!
 

Fellro

Moderator
Staff member
In a sense, he was right, in that it isn't full ABS, just rear wheel ABS. Even if the component was missing the diagnostic should give the code.
 

Kaajot

Micro Machine Manager
Aww. Nuts.

I'll install the new ABS Hydraulic Unit in and see if the code comes out, but I doubt it is and will pull the module again to get its correct part number and order a new one at that point.

Will read through my Chilton, any tips on the install or bleeds they won't have when the new unit arrives Saturday? I saw a guy bleed through his master cylinder on a Gen 9 recently, that's a new one. I always thought at the drums/calipers, but a couple posters said it's physics and air rises up (where this master cylinder is of course).

So I guess that's one way to do it?
 

Fellro

Moderator
Staff member
It may be the highest point, but there are other subsequent high points where it can get trapped.However, I have had success bleeding at the poont of replacement regarding things such as the actuator as there is a bleeder on top of it. The fluid down the line will remain, the wheel cylinders will remain full.
 

Kaajot

Micro Machine Manager
It may be the highest point, but there are other subsequent high points where it can get trapped.However, I have had success bleeding at the poont of replacement regarding things such as the actuator as there is a bleeder on top of it. The fluid down the line will remain, the wheel cylinders will remain full.

Nice!

That sounds like a good starting point. And yep, I get it, kinda like a P-Trap in plumbing regarding the bends and other high points where air would cavitate / fluid hold with air in an upper bend.

Doing an F-700 Steering Gear install tomorrow (rebuilt it, finally should not leak) and putting up my utility pole finally (in place), but will have this lined up to do next week or following weekend.
 

Fellro

Moderator
Staff member
A little cheater trick I use for avoiding as much bleeding is to have the bleeder screw open when you fill it, then lightly press the pedal to get the fluid moving. Sometimes you don't have to touch the pedal to get it to drain through. It naturally fills with fluid and cuts the bleeding time. With it in the middle like that, you want to avoid pushing the air farther back.
 

Kaajot

Micro Machine Manager
A little cheater trick I use for avoiding as much bleeding is to have the bleeder screw open when you fill it, then lightly press the pedal to get the fluid moving. Sometimes you don't have to touch the pedal to get it to drain through. It naturally fills with fluid and cuts the bleeding time. With it in the middle like that, you want to avoid pushing the air farther back.

Thank-you! That sounds like a good start to minimize my bleed time.

This is on my to-do-list by end of next week. Would have been Monday, but was told I had to start moving $180K in solar panels or lose them, so I'm moving them (about 6 truck runs 20 miles uphill each way). Solar contractor "broke" the panels and couldn't use them in their $1B contract, so I got 770 so far and about 600 more this week, priorities. They work, they just need to be sealed on the ones that work. The ones that got punctured through the silicon wafer will be scrapped (about 15 lbs aluminum each plus wiring for building custom panels and if one of the two wafer sheets isn't punctured, save that too.

We got the 1983 F-700 steering gear (that was rebuilt by a local guy out of a mis-ordered but VERY similar steering gear HFB-type) installed and it's not leaking! Of course the steering wheel is off-centered, so we gotta turn the spindle where we want it, disengage the steering column, straighten the column, and reattach it, but not leaking hydraulic fluid, FINALLY.

Also dropped the Utility pole lined up with its hole at the farm, so that's getting erected tomorrow. And finishing side flooring in chicken tractor to get about 80 cornish cross out to pasture, organic-fed only, with their very own Livestock Guardian Dog, Ripley. So a lot to do tomorrow, Monday/Tuesday and a VA appt and covid-19 test. :-( Think I got hit about a month ago helping install a soldier's 220v air conditioning line for $0, still don't feel right -- like I've been training for an ironman, nonstop, but i haven't. So they're trying to get that worked out and see if I got it and if I'm contagious or not.

Anyway, will take pictures when I get to the unit install. It's here! :) The old one is sooooo rusty brown. It looks like barnacles, never had a part on the truck that bad. Will try your trick to make bleeds less.
 

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