How does ABS work exactly? - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 10-22-2005
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How does ABS work exactly?

ok, this is a quite involved situation, dating back some 11 months and 15,000 miles.... 8 dealer trips... heh shoulda lemoned it but oh well, dont have the funds to really do that right now... and with school work and homelife, dont need ford fighting tooth and nail over this trucks issues.... so... i come to you with a few questions, to make a long story short, dealer has no clue wtf is wrong with this thing, a friend freind, suggested an abs problem, and suggested i disable it via the 2 fuses under the hood and see what happens... viola, disable the abs, truck runs like it just pulled off the lot... now, yesterday, 20 miles from hom, re-enabled the abs after 2 months of no abs.... nothing happened till today, its rained ALL day, sit at 35-40 truck cant decide what gear it wants to be in, its got pwr, but the torque isnt up to where it is with no abs.. so, im like 100% positive its the abs in my truck is like screwed... so, heres the questions...

1) I under stand abs pumps the brakes during hard braking to prevent lock ups (i can lock my rear wheels regardless of wether or not i have abs, as long as its wet out, i can lokc the rear) does abs kick on under "normal" braking?

2) whats an abs motor and whats it do?

3) I understand that abs has a transmission solenoid to down shift the tranny in extreme cases, what causes this to occur? what has to happen for the abs to say "hey, i better down shift in order to slow down"?

4) Where is the abs motor, and the abs solenoids located?

5) how do abs kill switches work? and whats the benefit to killing abs? besides the obvious

ok those are my questions.
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Old 10-22-2005
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Well, I'll take a crack at it. Bob (rwenzing) can enhance or correct what I say as I think he knows a lot more about it.

1. ABS looks at what speed you're traveling at, and whether or not your wheels are turning at a speed close to that. When either front wheel starts to lock up, or BOTH rear wheels lock up (you can really only sense the ring gear which only stops when BOTH wheels do), the ABS system fights the brakes back to unlock wheels. It unfortunately backs off ALL the brakes. Our system is called "3 channel, 4 wheel" ABS. You can lock up one rear wheel and not the other and the ABS may not be able to tell.

2. The ABS motor provides the "power" to back off the brakes with counter hydraulic pressure -- or so I believe -- BOB, HELP! I can look it up if he doesn't pop in.

3. I know nothing about this item. I'll see what I can find in the service manuals, but I only have manuals up to 2002 and yours is the quite-redesigned 2004.

4. Under the hood, on the firewall on the drivers side. It has a bunch of hydraulic lines (5 I think) coming into it, and an electrical connector. It is located between the battery and the engine compartment fuse box, right over the left front wheel. It generally has "4x2" or "4x4" stencilled on it also, from the ones I've seen. Don't know why they're different. There is a separate electronic control unit, but I'm not sure of it's exact location.

5. ABS kill switches work by fooling the ABS system into thinking the key is off. At least, that's how most of us do it. I simply pull fuse 14 in the passenger compartment (again, don't know about a 2004) to kill the ABS. This is "switched" power and without this signal, the ABS system won't work and the indicator will light to tell you it isn't. The benefit is only under conditions where ABS hurts, like offroading where you may have wheels in the air that could lock and cause ALL your brakes to back off just because you have a wheel in the air. Not fun. Easy to lift a front wheel with IFS and limited travel. Pickup trucks, with their light rear ends, are subject under street conditions to total rear lockup and then they lose traction in ALL directions in the back and that can cause a spin. It's really better to have ABS on the street.

That's my first crack at answering.
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Old 10-22-2005
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well heres the defenition straght from my drivers ed book (dunno why i still have it lol )
an acronym for anti-lock braking system. This is a supplemental braking system that works with your conventional brakes to aid in steering during and emergency stop.

so basicly it jsut allows your car to ramain in control by not allowing your wheels to fully stop spinning, but still supplying braking power
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Old 10-22-2005
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anyway to just disable just the front ABS?
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Old 10-22-2005
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Hmmm...I'd have to think about that. I don't know that it's easy to do that as you'd somehow have to fool the system -- maybe by "repeating" the rear ABS signal into the front channels...need to ponder.
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Old 10-22-2005
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well, my reasoning is, lst time i changed my rotors, they came with a different sensor ring, now when i use my brakes, you can feel the abs pulsing the brakes, now either i managed to dirty up the sensor or the abs doesnt like the different styled sensor ring

however I havent had the time to mess with it, and if it was something simple to just disable the front abs that would save me a headache



Ill be pulling it all apart when i lift it, but i didnt plan to do it anytime soon
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Old 10-22-2005
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I looked up the 2004 circuitry and could find nothing to support the notion that the transmission downshifts to somehow "assist" the ABS system. There appears to be no electrical connection between the transmission controls and the ABS unless something is being done over the Module Communications Network. My first instinct would be that downshifting would be exactly what you would not want to do.

The brake system on your Ranger is designed to be used with the ABS operational. Without it, there is no front-to-rear proportioning. I can tell you from personal experience that my Ranger is much more difficult to control on pavement with the ABS disabled.

I don't know a great deal about ABS, so I'll just post what the 2002 Ranger shop manual says about it. I wouldn't think that it has changed substantially since then.

Quote:
The ABS operates as follows:

l When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the HCU inlet ports. This pressure is transmitted through four normally open solenoid valves contained inside the HCU and then through the outlet ports of the HCU to each wheel.

l If the anti-lock brake control module senses a wheel is about to lock, based on anti-lock brake sensor data, it closes the normally open solenoid valve for that circuit. This prevents any more fluid from entering that circuit.

l The anti-lock brake control module then looks at the anti-lock brake sensor signal from the affected wheel(s) again.

l If that wheel(s) is still decelerating, it opens the closed solenoid valve for that circuit.

l Once the affected wheel comes back up to speed, the anti-lock brake control module returns the valves to their normal condition, allowing fluid to flow to the affected brake.

l The anti-lock brake control module monitors the electromechanical components of the system.

l A malfunction in the anti-lock brake system will cause the anti-lock brake control module to shut off or inhibit the system. However, normal power-assisted braking remains.

l Malfunctions are indicated by a yellow ABS warning indicator in the instrument cluster (10849).

l The anti-lock brake system is self-monitoring. When the ignition switch is turned to the RUN position, the anti-lock brake control module will carry out a preliminary self-check on the anti-lock electrical system indicated by a three-second illumination of the yellow ABS warning indicator in the instrument cluster.

l During vehicle operation, including normal and anti-lock braking, the anti-lock brake control module monitors all electrical anti-lock functions and some hydraulic operations.

l Each time the vehicle is driven to approximately 32 km/h (20 mph), the anti-lock brake control module turns on the pump motor for approximately one-half second. At this time, a mechanical noise may be heard. This is a normal function of the self-check by the anti-lock brake control module.

l Pedal pulsation coupled with noise while braking on loose gravel, bumps, wet or snowy roads is normal and indicates correct functioning of the vehicle's anti-lock brake control system.


Hydraulic Control Unit

The HCU consists of the following components:

l brake pressure control valve block

l pump motor

New brake pressure control valve block and pump motor are installed as an assembly.


Anti-Lock Brake Control Module

Note:
The anti-lock brake control module is 4x2 and 4x4 specific. Do not interchange modules.

The anti-lock brake control module is mounted to the HCU.

It is an on-board diagnostic, non-repairable unit consisting of two microprocessors and the necessary circuitry for their operation. The anti-lock brake control module monitors system operation during normal driving as well as during anti-lock braking.

Anti-lock brake module operation is as follows:

l Under normal driving conditions, the microprocessor produces short test pulses to the solenoid valves that check the electrical system without any mechanical reaction.

l Impending wheel lock conditions trigger signals from the anti-lock brake control module that open and close the appropriate solenoid valves. This results in moderate pulsations in the brake pedal (2455).

l The anti-lock brake module used in 4x4 application includes a G-sensor. It detects vehicle movements during a brake lockup event that is transferred to other wheels through the powertrain.
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Old 10-23-2005
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I can't fathom what on earth would be causing the drivetrain to act stupid when the ABS has power. I'm as beside myself as John and Bob. They shouldn't be effecting eachother. It's rather obvious that the ABS has something to do with it if the problem goes away when you remove power from it.
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Old 10-23-2005
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I was going to edit my post last night, but for some strange reason i couldnt access the site at all... the OTHER thing that is dead obvious WITH abs engaged is this: HARD shifting. jerks when downshifting. like cruising at 45 then slowing and stopping for a red light. itll hard down shift... if thats the right terminology..... i noticed this yesterday while cruising around with the abs on.... and it runs funny... like i said in my original post. now, i said screw this and disabled abs, again, and like i said, ALL these symptoms... vanished! so, i think ima call the dealer tomarrow am, or go down their and talk to them.... with abs disabled, its like a brand new vehical..... without abs itll put u back in the seat from a stop ..... with abs, eh, itll put u back, but its like, not the same... if u know what i mean

could the trucks computer be causing this? I have come to the conclusion that the "diagnostic lights" and codes on these vehicals are total bs.. and dont do anything other than rack up huge amounts of cash for the emissions people... like, could the computer be over compensating or something? because when u erase the puters memory, WITH abs enabled, truck runs great for like a week. then it all comes back....
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Old 10-23-2005
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Which fuses did you remove from the Battery Junction Box to disable the ABS?

Do you ever get an ABS light when the ABS is functional. If so, what was the Diagnostic Trouble Code?

Check the condition and security of all of the underhood ground points:
2 eye terminals on the inner fender near the Battery Junction Box.
2 eye terminals on the radiator bulkhead in front of the battery
1 eye terminal on the passenger side inner fender near the speed control servo.
1 eye terminal on the fiewall bulkhead near the large 104-pin PCM connector.
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Old 10-23-2005
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never got any trouble codes.... but get this, at 5500 miles on my way home, maybe 25 miles from home, i came up on a toll booth on the thruway, doin bout 50, cold rainy... tapped the brakes and locked up. *** fishtailed, took my foot off the brake and they unlocked.... dealer solution: replace the rear brakes. i can also lock up the rears on wet pavement WITH ABS engaged.... figure that one out. heh. and last xmas while i was out playing in the slow in parking lots, i locked em up... thought abs wasnt supposed to allow that?

anyways, no trouble codes on the abs, tho, according to their little black box they put in my truck a few times, the torque converter slips or locks up, causing the truck to "buck" im pretty sure they fixed that cause it doesnt do that anymore... now, it just downshifts hard, has like, not as much power, and cant decide which gear it wants to be in between 35-40mph... with abs disabled, it shifts at 43mph.
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