Hey all, so the problem I am having is that at very low speeds say between 2-10 mph, while braking, the ABS kicks in and I get a slight shudder in the brake pedal and there is a slight grinding noise. I can't tell which wheel is affected. Scanned my truck and I don't have any codes. It's so annoying that I hate to drive now. I figure one of the sensors is probably bad. I know how ABS works but why the grinding noise? It sounds like the shoes/pads are worn down but they aren't, so what could be grinding?

 

Do you have a lit dash ABS light? If so & you have a ELM327 scan tool, load FORScan diagnostic software on the viewing device of your choice & have it perform a vehicle trouble code scan. It can have a look into All of the vehicle computer/controllers for pending, or set trouble code clues, then post All trouble code Numbers.
The ELM/FORScan combo can also put up on the viewing device, its dashboard live sensor feeds of our choice, to monitor various things during a trouble shoot.

On the grinding noise, if the pads/shoes linings are ok, you could have a small imbedded stone in a pad, rotor rust, or maybe a hard section of lining, or pad, causing the noise.
We just went through such a grinding noise & with intermittent pulsation on the Wife's 2000 Neon, with the right rear wheel rotor/pad.
I put new ceramic pads & new rotors on, flushed & bled the system with new Motorcraft DOT-3 brake fluid & all is now quiet & braking is smooth, no more intermittent pulsation & no more grinding noise after bedding in the new pads/rotors.
The old pads & rotor looked ok, no cracks, chips, glazing, or other obvious defects noticed. These old pads were Advance Auto Gold series pads & never were as quiet as the OEM pads, but were Much cleaner. The Gold series I noticed were made in India, so that may have been a clue, if the pad material wasn't mixed evenly before firing, it could have had a hard seed that it finally wore down to & exposed???? Or maybe the OEM rotor had a hard spot exposed by wear?
Anyway I chose to try the Advance Ceramic recipe pads for the rear, as I had put their Ceramic pads on the front a few years ago & they are doing fine. Smooth, quiet, clean.

Some thoughts for consideration, do the ELM/FORScan trouble code scan & let us know what you find.

 

Actually the grinding (which actually sounds more like scraping metal on metal) only occurs when the ABS kicks in. Since the ABS only kicks in on very low speeds while braking the scraping last only a second or two before I come to a stop. I understand how ABS works but I wonder what could possibly be scraping. I just had my rear drum brakes looked at and adjusted in case that was the problem, but it didn't help.

I own a BlueDriver bluetooth scanner and I don't get any codes even pending ones. I've watched a couple of YouTube videos regarding this exact problem that Im having. I guess I will have to brave the cold and get under the truck and look at my sensor and/or wiring.

This is my exact problem: I just have the additional scraping annoyance which he doesnt talk about.

 

Ok, as I mentioned earlier, the inexpensive but powerful ELM & FORScan as discussed here https://www.ford-trucks.com/forums/1...-scantool.html, can put up the ABS speed sensors in graph form, so you could see which sensor has the drop out problem & save you some time. Also check the sensor for metal debris which could affect it's sensitivity, as well as tone ring for debris, or damage.
Also if it's a front wheel, check for excessive wheel bearing play & adjust if wheel is loose.
Did the scraping noise & ABS acting out come about suddenly after some event & at the same time, or was each a separate event?
More thoughts for consideration, let us know what you find.

 

I know you promote FORScan alot but I just bought my scanner and am not able to go out and buy another one. My scanner came up with an Brake ABS code C1939--Brake Pressure Switch Input Circuit Failure. Is that the switch located on the Master Cylinder?

 

C1939 is for a under hood brake master cylinder pressure switch Circuit malfunction. Could be a switch, electrical connector, wiring, or fuse problem.
Check the fuse first, then use your multi-meter to see if you have B+ voltage To the switch, if not then check the wiring for continuity/open circuit, between the fuse & switch.
Could be a connector problem if any are between the fuse & switch.
If all that checks out, then block the bake pedal so the brakes are applied & measure B+ on the other side of the switch, if none, put the switch high up on the suspect list. Maybe try & thump it, to see if it'll wake up. If no joy consider replacing the switch & let us know what you find.

Yup the inexpensive ELM scan tool, running FORScan windows freeware, or inexpensive smart phone FORScan, that's tweaked for Fords, or a like diagnostic software, sure are nice, inexpensive but Powerful diagnostic items for our electronic tool box. SO I try & encourage their use, as they can save us time & Way more than their cost!!!
They did for me in their First use on my 99 Ranger ABS & power window woes trouble shoot!!! Led me right to both problems by finding GEM trouble code clues I didn't know I had, that properly focused my trouble shoot, all that sold me right on the spot!!!!

 

I am having a similar, but not exact false abs activation's as you.

If you already have the scanner, you probably only need to get the ford software

My software that I was using with my bloothtooh scanner did not show much, but what he is recommending is just the ford app that can give you better info (I was using torque). It was under $5.00 and yes it did give much more detailed info. There is a free version you can test first to make sure it's compatible with your bluetooth dongle.

So you may want to check that out as it may only cost you $5.00 more to use the ford specific software.

My gf is presuring me to just take the truck to Ford, but I have the day off today so finally going to see if I can figure anything out first.

Good luck!

 

Hi pawpaw,
I have a similar issue on a 2001 Ranger Edge 4x2 4WABS. I was getting the symptoms described but no code. Front left tire was locking up but ABS pump was working the front right. Causing a spongy pedal and poor brake response. Back when I first encountered this over a year ago, I needed to replace wheel bearings so I replaced the hub/rotors and pads while I was at it and cleaned the ABS sensors and any corrosion from the hole in the knuckle it is mounted through. Now the problem has come back and the bearings need to be replaced again.

Changed front right ABS sensor while doing that side's wheel bearings and code C1939 showed up immediately. Cleared with FORScan and it comes back. Read ABS sensors and getting a signal drop on the new sensor at low speeds. Found the attached Service Manual instructions to troubleshoot C1939 on Just Answers but part of it calls for a Breakout Box which I have no idea as to what this is and I cant find any wiring diagrams to identify the connectors it references.

Any suggestions as to what else to try? I was going to check the back of the knuckle to make sure the sensor is getting seated all the way and do the other side bearings and sensor tonight.

 

Did you opt for a OEM sensor? Is it installed correctly so its in the proper position?
If all that is ok, since you've had so many wheel bearing problems, which is unusual, check the new sensor & tone ring for damage or debris & the wheel bearing for unusual / loose play & if found properly adjust the bearing.
If all that is ok check the sensor electrical connector contacts for damage or corrosion & the wire run for damage. Check the wire run resistance to the pressure switch & wiggle it while testing.
Check the ground side of the wiring run all the way to the battery B- post, for more than the 5 ohms Max resistance the service manual calls out. Do it with a wiggle test of the wiring run & ground connections. All ground connections, all the way to the battery B- post need to be clean, bright & tight.
If all that checks out ok, have you performed the tests in my post 6, or the tests in the manual you posted up to the break out box comment? The break out box is just a test box that allows us to make easier test measurements, but we can work around it, or build our own if you want to take the time to do that.

Btw what Color is the brake master cyl pressure switch Insulator, that surrounds the center contact??? Black color is good. Rust red color makes it a questionable switch.

On the soft brake pedal feeling when the ABS triggers, have you ever let air into the braking system during repairs, or when flushing the system with new fluid, such that air may have gotten into the ABS motor valving?

Some beginning thoughts for consideration let us know what you find.

 

Is this what you're referring to about the questionable switch color??
https://drive.google.com/open?id=1Py...cc2zOkbZ5wePE5
https://drive.google.com/open?id=1fP...dE4cR1fGs7D1_p

I got the sensor from Autozone and according to FORScan, the signal drops out until I get to about 10 mph. However at about 10mph is also when the ABS light comes on. Could I have an out-of-spec sensor?

Bearings are brand new. Installed at the same time I replaced the sensor and cleaned the tone ring which wasnt really dirty at all. Thursday night.

Checked voltage on Friday before I posted, I have voltage to the switch. If I recall correctly, I did B- to yellow wire. Voltage goes away when brakes are applied. I'll check the continuity on the other wires now. Any chance you could tell me what wire colors go where? I am unable to find a schematic.

If I change the pressure switch, will I then need to bleed the ABS motor?

Thank you for your help. Greatly appreciated.

 

So did some poking around:

B- to yellow wire on BPS always hot
B- to green wire on BPS no voltage when brake applied/hot when no brake
BPS terminals (wires disconnected) Brake applied - no continuity
BPS terminals (wires disconnected) No brake - continuity 0 ohms
I think this tells me the BPS is fine???
Re-installed old ABS sensor FORScan show same symptom of signal dropping (spun tire by hand, had good reading from other side tire spun by hand)
Both terminals on ABS sensor connector have continuity to harness going into ABS module (Yellow/Red Stripe and Yellow/Black Stripe)
Could it be that the tone ring is bad? I replaced the whole hub a little over a year ago.
Could the knuckle/spindle be damaged causing enough of a wobble to loose signal?
If there was that much wobble, wouldnt I feel it driving or see it spinning the tire?
Checked the back of the knuckle, sensor appears to be fully seating.

We're about to sell it very soon, just dont feel very good selling a vehicle with brake issues.

Thank you!!!

 

Pawpaw, I came across another thread that someone had found that their tone ring had been pressed on too far and the gap was out of spec. Do you know if it is possible to adjust the tone ring or if I find this to be the case, will I need to replace the hub again?

 

Have you been opting for OEM hubs sensors, wheel bearings, or least expensive aftermarket parts?

 

Napa quality seems good enough imo for these light trucks. I would not put the cheapest amazon Chinese hub on my truck.
I just replaced a sensor on my 96 4x4 ranger as well as bearings,axle u-joints,brakes,rotors,seals and ball joints . The doorman aftermarket sensor would not fit in the hole without beating it in so i picked up ford one. I had to unplug both sensor wires until i got the ordered ford part as my brakes would jerk at slow speeds with only one sensor working. With them unplugged the brakes seemed fine, just no abs. You could unplug them to see if it keeps jerking. If it does its not the sensors and you can move on to the stuff that gives me a headache.