So annoying. I wish I could pinpoint the problem at this point but I'll try and explain.



NEVER had the ABS light come on in the 5 years of driving the truck daily. I did replace the rear ABS sensor to a Raybestos one years ago. I replaced it again for an OEM Ford one only because the Raybestos connector doesn't click like the OEM one does on the sensor. I did a bunch of work to my truck months back, which included changing out the rear diff cover to a larger one.

Now when I drive I can go sometimes 100+ miles or a tank or two and then my ABS light will kick on the dash and stay on until I turn the truck off. At which point if I turn the truck on it will go through the ABS check and the light shuts off and it's fine.
If I unplug the sensor while the truck is on the light comes on instantly. Shut the truck off and then plug the sensor back in, and the truck does it's test and the light goes out. I've checked the wires and everything and there does not appear to be a short anywhere. I believe this also because if I take the sensor out of the axle housing and move the wiring all about more than what would normally happen with the suspension not ABS light comes on... but again, will come on instantly when I unplug the sensor.

Would having a larger rear diff cover cause problems like this? Note that when I pull the codes it indicates a rear sensor.

So I replaced the rear sensor again with another OEM Ford, and that seems to have helped in the sense that it doesn't happen as often but the fact that I shut the truck off and then start it back and the light is off, tells me it's not the sensor?

I am thinking about buying a new Raybestos sensor just because I never had any issues using one for 5 years and then after I switched to OEM sensor have a random ABS light come on.

I also changed out the front ABS sensor/cruise control switch on the master cylinder block along with a new harness... I hate throwing parts at things but these two items are cheap. It just gets annoying if I buy the same sensor x3...$60..etc. That's annoying to me..lol

What else could possibly cause this? I've checked with my scanner and when the rear end is up. I can see that the ABS sensor is in fact sending a speed of the rear wheels. I check the front wheels and each sensor also sends a speed/single.

This ONLY comes on when I am going slowly or stop and go type of traffic when I go from a slight crawl to almost no speed... but again doesn't happen all the time. Today it happened going to work when I was stopped and maybe going less than a mph... then I shut it off and turned the truck back on and didn't come back until coming home and stuck in stop and go crawling type of traffic....

At a loss as to what else to check/do. The fact that the light shuts off after it's check has me stumped since it's not a constant ABS on light no matter what is done...


-Nigel

 

This is the error I am getting on FORScan. Makes me wonder since I already replaced the ABS switch on the master cylinder to a new one, which came with a new harness.

-Nigel

 

Brake pressure switch is normally Closed
When you press down on the pedal, pressure in the master OPENS it

The switch gets 12volts with key ON, and that 12volts goes thru the switch to ABS module, until you press down on the pedal, then 12volt is cut off.

The ABS module also gets "brakes on" signal from the pedal switch, which is normally OPEN, so it should "get" 12v from this pedal switch, at the same time is "loses" 12v from pressure switch

Thats the only way I can see it setting that code
If pedal switch is loose it could be sending 12v to ABS module but no loss of 12v from pressure switch at that time.

 

I will check the pedal switch after I am done with work today. And I was also getting a rear speed sensor error. I swapped that above the diff twice now and still keep getting hit or miss.. Not sure why honestly. I don't know if it's because I have an extended diff cover but that really shouldn't affect anything I would think..?

I had checked the harness up front that connects to the master cylinder/switch and all was fine, and I got connectivity and had power to it.

Yesterday I drove to work and it was stop and go traffic, no ABS light came on other than when the truck was started and it did it's check. This morning I start the truck and put it in drive. ONLY coasting on a flat driveway for about 30 feet the ABS light comes on. Mind you I am only going 1mph or whetever the engine is pulling me.

Get to the stop sign, shut the truck off, turn it back on and ABS light doesn't come on rest of trip to work...

I will note that when I use FORScan to test ABS it comes on and pumps and registers back with no problems and the test was successful.

-Nigel

 

Reads more like wiring connection issue than "device" issue

2001 ABS wiring below
Deactivation switch is(should be) the pressure switch on master cylinder and in this diagram it shows it as OPEN when no brakes are applied
When brakes are applied ABS sees 12v

Brake pedal switch also needs a GROUND to send to ABS Module when no brakes are on, I guess thats to confirm switch is working, so GROUND when pedal is up and 12v when pedal is down, not just 12v on or off, must be Ground or 12v

 

Thanks Ron! You never cease to amaze me with the amount of knowledge you have!

I will have to check this out today when I get home. Drove to work today and no ABS light came on at all and I was trying to replicate the problem that I had just to see what would trigger it. You might be right in terms of wiring problem.. which would suck because chasing electrical gremlins are no fun...

I'll see what I can fine today.

-Nigel

 

I didn't realize the brake pedal switch for the ABS side needed to be grounded, I just thought is was 12v on or off, like the brake lights
So you learn something new everyday

 

Did you ever find the issue, my truck 99 ranger does exact same thing, all sensors are good, sometimes at low speed (crawl) lght comes on I shut off truck and it resets and does not come on again until next crawl incident ??...Thanks

 

I replaced the OEM rear sensor back to rybestos and never had the abs light come on..lol

Hate to say perhaps the truck didn't like it, but honestly I can't think of any other reason? I went through two OEM sensors which gave the same results. Switched back to rybestos and haven't had it since nor any cel. Take it with a grain of salt I guess?

-Nigel

 

Good to hear.

Ltr

 

OK My light came on today again 2 times NO reason, going slow....what was the Raybestos part number you used....Thanks

 

Raybestos ABS530780 Sensor