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ABS light coming on intermittently. #: 798

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Posted: Thu Apr 19th, 2018 04:27 pm

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NewShockerGuy
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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

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Posted: Thu Apr 19th, 2018 06:12 pm

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What fluid did you use in the rear? Its probably a long shot (a very long shot), but the difference in magnetic properties could cause issues.

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Posted: Thu Apr 19th, 2018 06:38 pm

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NewShockerGuy
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Used Amsoil synthetic 80w-90 gear fluid:
https://www.amsoil.com/shop/by-product/gear-lube/synthetic-80w-90-gear-lube/?code=AGLQT-EA

Used this multiple times before and didn't have issues. I don't know why for some reason I still think it's possibly the sensor. I wish I never threw out the working Raybestos abs sensor.. I had it in a box and then said I don't need it after I replaced with the ford one. I guess when I get the sensor in a few days I will swap it and just see what's going on. Arg... so bloody annoying.

Would having an extended diff cover cause any problems? I can't see how it would but makes me wonder?

-Nigel

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Posted: Thu Apr 19th, 2018 06:41 pm

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NewShockerGuy wrote:
....What else could possibly cause this? I've checked with my scanner and when the rear end is up. .....At a loss as to what else to check/do. .....

No idea what scanner you're using but if it itsn't FORScan then using it is the next step. FORScan because, it pulls not only the OBDII DTC's but more importantly, the extended/proprietary to Ford DTC's.

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Posted: Thu Apr 19th, 2018 07:20 pm

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I'd be curious if the tone ring in the diff is dirty. The larger diff cover and diff fluid shouldn't have any effect, but missing teeth, or something stuck between the teeth on the tone ring can cause issues.

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Posted: Thu Apr 19th, 2018 08:07 pm

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NewShockerGuy
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I have an Autel Scanner MD802 Maxidiag Elite.
https://www.amazon.com/Autel-MD802-Maxidiag-Diagnoses-Transmission/dp/B0090B7M2O

I also was using FORScan.
Exact code comes up via the DTC as the following:C1939 - Brake Pressure Switch Input Circuit Failure
ABS light is not on, nor is any CEL light on...

EDIT: I will note I found a thread about this code.. Someone suggested warped rotors... I WILL note that just lately I have noticed that when I apply the brakes I can feel a shuttering motion. AS if the rotors are warped in a way. If I let go of the steering wheel I notice that it shimmies (not much) left and right, but you can definitely feel the truck doing a sort of squirm, shake motion when braking. More so from a moderate pressure.

-Nigel

Attachment: brake problem.JPG (Downloaded 47 times)

Last edited on Thu Apr 19th, 2018 08:11 pm by NewShockerGuy

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Posted: Fri Apr 20th, 2018 11:05 am

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I can't remember what MY your Ranger is, but anyway, I went and looked in the FSM for an 04 and unfortunately there is no C1939 listed nor is there a symptom that is similar to you've described. Went digging for info on that DTC and (probably) found that same post on the warped rotor but there was no final fix and conclusion. I did come across a couple references to the switch mounted on the MC, but this is where the MY of vehicle may have mattered. RE the axle cover and fluid, realizing that the tone ring and sensor generate a square wave and it's the location/relationship between these two parts that matters, and this isn't user adjustable, I wouldn't expect that the cover and especially the oil could impact operation. I do recall over the years that there is some history of 93ish through late 90's Rangers having sensors go bad in the rear axle, and although they wouldn't trigger the CEL another symptom was prestent, could be odd shifting, could be RABS light came on, and IIRC sometimes the CC was acting up, and when this was the case the only way to confirm the sensor was bad was to do what you and I hate......throw a new part at it (hey, at least it's an educated guess). So with that said and seeing how many different sensors you've been through (and if your MY even applies), it's probably safe to rule that one out.

May not have an answer but I've got a few ?'s

* what MY?
* ABS or RABS?
* when the light comes on do you have your foot on the brake or are you just rolling along and out of nowhere, on comes the light?
* I read the OP but.....do you recall any connection between when this began and any work you did soon before that?

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Posted: Fri Apr 20th, 2018 02:15 pm

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IIRC, Nigel has a 2001 Ranger.

C1939 is for an electrical problem in the Deactivator Switch (Brake Pressure Switch) circuit. The DS screws into the front of the brake master cylinder and is involved in the operation of the speed control (many Ranger years) and the ABS (2001~2003 Ranger only).

The Deactivator Switch was subject to recall for 2001MY Ranger as well as several other model years and also other Ford vehicle lines. In service, the diaphragm in the OE Deactivator Switch may rupture and leak conductive brake fluid internally onto the switch contacts, thus providing a path to ground through the fluid in the brake master cylinder . Worst case scenario is overheating of the flammable fluid leading to a vehicle fire. Depending on the year and vehicle line, this can even happen when the ignition switch is in the "OFF" position and the vehicle has been left unattended for several hours or days.

The recall repair for 2001 Ranger consists of a replacement Deactivator Switch (from a different vendor) and a small patch harness which contains a dedicated 2A fuse for the DS circuit. (2003 and later Rangers had the fused circuit integrated into the original harness and fuse panel.)

If the recall action has not yet been performed, I would start by having it done immediately (Recalls stay in effect indefinitely).

If the recall has already been done, I would first check the condition of the patch harness connectors and fuse. Then move on to the Deactivator Switch itself.

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Posted: Fri Apr 20th, 2018 04:13 pm

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Very good information so far. I hvae a 2001 Ranger XLT RWD. I can say that I have never seen the ABS light come on before in the 5 years other than when I turn the vehicle on and then it shuts off after the test.

I checked all wiring and jiggled everything while my wife was in the truck to see if the rear sensor wiring was messed up. IE: If it's a broken wire, me pulling/pushing the loom is bound to do something if it's a problem like that. I did that for 5 minutes and nothing changed in terms of ABS light coming on.

My truck already had the recall done. Though they had the older switch on there I just replaced the switch and harness with a new one maybe two weeks ago. I had the bed off when I was doing the fuel pump months ago but when I looked at everything nothing seemed out of the norm. When I changed diff covers I cleaned the inside of the diff with brake clean like I normally do and there was no metal/shavings/anything out of the norm at all. Put new diff cover and filled it up. The ONLY thing I did differently was since the bed was off I filled the diff up at the sensor hole on the top rather than the fill port. BUT I had the fill port open so when fluid started coming out of that I then closed it up. (It was just easier pouring it from the top than from the awkward sideport)... I changed the Raybestos sensor to the OEM one. Then slowly driving out of the driveway/street the ABS light came on.

Pulled into the driveway and checked and when I turned the truck on it was gone so I figured it was a fluke. Got the truck inspected and it was fine and then driving back after going over a speed hump it came back.

I will note that the ABS light came on today and it was from about a stop to a 2mph then stop again situation. Makes no sense. I pulled the code and it was the faulty brake switch listed above.

I checked all harnesses. I took the recall harness off, checked fuses, checked connectivity. and checked volts. All pass and no broken or frayed wires. Putting out 12v when the truck is on.

I did just bleed the master cylinder while I was there, it spit out some dirty fluid and maybe an air bubble or two..nothing major. I never bled the master cylinder before, always just at the front/rear brakes.

I would say the light does NOT come on when I brake at all. In fact I can hard brake, light brake..etc. Light will not come on. It's usually happening when I am fully stopped and or rolling slowly in a stop and go situation. But again, never had this problem and I was for many years in stop and go traffic morning/night so I would have noticed this happening. I don't want to say I did anything while working on the front of the truck but it's just odd. Really odd.

Just ran FORScan after I got home and shut the truck off/turned on and nothing pops up. Did the ABS test and that's successful with no DTCs...lol Of course.

This is odd, and annoying. I'd rather the light be on all the time honestly then it might be easier to diagnosis. I am going to bring my scanner with me tonight when I go out and have the wheel speed sensors running on it to see if everything is matching.

I know when I test the brakes and push the pedal it reads instantly on/off depending on if I am pushing or not, so I know the switch inside/obdII is reading it and registering the info.

-Nigel

Attachment: brake2.JPG (Downloaded 39 times)

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Posted: Fri Apr 20th, 2018 04:54 pm

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It seems that you are concentrating on two areas: the Deactivation Switch on the MC and the ABS Sensor on the diff. If it is coding C1939, what else is there that points you to the axle sensor?

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Posted: Sat Apr 21st, 2018 06:59 am

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Sorry about that. I was in those two areas because I kept getting a rear speed sensor error. That was the initial error I was getting, so I swapped out the sensor, but then it came back.

So no light at all yesterday going to work. I was in stop and go traffic. This morning I start the truck. ABS light does it's check and goes off. I put the truck in drive and only start to coast and within 30 feet m ABS light comes on. I get to the stop sign, shut the truck off, turn it back on and it doesn't come back on the entire trip...

So I'm not 100% sure if things are related or not with two of them.

-Nigel

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Posted: Sat Apr 21st, 2018 09:59 am

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Here's something that should be checked whenever there is a mystery electrical problem in the rear half of any 2000~2003 Ranger.

Underneath the truck, directly below the driver seat, there is a large electrical connector held by a captive bolt with a 10mm hex. Loosen the bolt from below, open the connector and look inside for water and/or corroded pins.

This connector lives in a hostile environment and serves everything to the rear of the cab: rear lamps, fuel pump assembly, evap controls and rear axle sensor. It can potentially be the source of open circuits, intermittent open circuits or unintended current flow between circuits. Even if you don't find any existing problems, it is a good idea to repack with dielectric grease before reassembly. This should be a preventive maintenance item on any 2000~2003 Ranger.

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Posted: Mon Apr 23rd, 2018 08:10 am

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I will check that connector today when I get home from work.

Drove to work today and it was fine, no ABS light came on at all. I even went slow in certain parts just to see if I could trip it. Nothing...

I hate these types of problems because it's hard to find/replicate if it's not a constant on type of deal... arg.

I'm wondering if I possibly pinched something when I took the front valve cover off and had to move that bunch of wires on the right side of the engine away...

That's the only thing I can think of since the rear end with the bed off nothing was touched in terms of wirings/or looms. I simply disconnected the rear taillight/trailer harness but that wouldn't affect the rear abs sensor.

-Nigel

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Posted: Mon Apr 23rd, 2018 09:25 am

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Just in case my previous post was not clear ... you access that connector from under the truck, not from inside the interior. It is a bulkhead connector in the sheet metal floor of the cab and connects the cab interior harness to the rear chassis harness that travels down the left frame rail. Should be a very easy check.

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Posted: Mon Apr 23rd, 2018 09:58 am

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Some great advice I will remove mine next time I am under there and use this:

Which is what I use on pigtails for lights even when I put LED's in. Good stuff unless V8 Level II has another brand he recommends.

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Posted: Mon Apr 23rd, 2018 12:09 pm

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I use Ford's dielectric grease on brake pins and electrical connectors. That's just what I happen to have. Any quality brand of silicone dielectric grease should work equally well.

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Posted: Tue Apr 24th, 2018 08:08 am

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Checked the connector and no corrosion at all which is good. I put some dielectric grease on the pins just for safe measure and connected it again and made sure the bolt was tight.

Swapped out the rear sensor back to the Raybestos one just to see what would happen. I haven't had the rear speed sensor error come up. But keep getting intermittent front ABS sensor errors meaning at the master cylinder. Yet when I run through the tests/diagnostics using FORScan and my code reader it comes back as ABS passed, no faults.

I'm wondering if there was a wire or something that was moved in a way. There is that bulk of wires right on the right side of the engine that attaches to a clip on the intake manifold. I did remove/move that to get the valve cover/intake manifold off the truck when I was doing work... I will have to check that again.

Drove the last two days with no errors..

Could brake calipers cause that message? IE if something was internally wrong/plugged with them? Seems out of the norm only because I bled the brakes and had no issues nor was there any problem with fluid flowing..

My rotors are somewhat warpped/or pads not right only because when I brake I can feel the truck shimmy and the steering wheel when you let goes slightly does a left/right shake, which tells me it's definitely the front brakes. What's weird is I just did an entire brake overhaul 2 years ago. This has been the only vehicle that I have replaced brakes/rotors often. Seems like after awhile that shake comes back.... not sure why?

-Nigel

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Posted: Wed Apr 25th, 2018 01:05 am

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I just want to add to this. If you are viewing the Brake Pedal Position PID in Forscan (under PCM) then it is reading the signal from the electrical switch on top of the brake pedal. If you are getting good ON/OFF viewing this, it isn't telling you what the pressure switch on the master cylinder is doing.

The PID you need to look for is Brake Pressure Switch (BPS).

Here is a thought. If you have cruise control, disconnect the servo connector. The brake pedal position switch "signal" comes out of the switch and splits to the cruise control module/servo and also to the PCM. Something could be going on with the CC and is bringing the voltage down or something along those lines.

I'm wondering if the code setting criteria is checking a correlation between the brake pedal position switch and the brake pressure switch. If the two values don't match it sets a code based on the one that doesn't. Either that or it is seeing a voltage that is neither battery voltage or whatever the non-brake applied voltage is.

If you want a half-A$$ed fix, you can just jump your brake pedal position switch over to the pressure switch wires and disconnect the pressure switch. It's there for redundancy for Cruise Control deactivation. When I added all the power options to my truck around 2010, I never installed the pressure switch and just jumped the wires. Granted this is only on a RWABS system, so I cannot vouch for ill side effects on a 4WABS system.

Last edited on Wed Apr 25th, 2018 01:08 am by sheltonfilms

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Posted: Thu Apr 26th, 2018 07:54 am

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Don't have cruise control on the truck. Other than this switch and harness that was replaced no other components of cruise control were installed by anyone or the factory. I checked other things using my scanner. For some reason I can't really see that much with FORScan as I can with my scanner. The brake switch activates no problem via on/off and no matter how I touch the pedal it registers.

I swapped out the rear abs sensor on the axle housing back to the raybestos. So far I've been driving for 3 days and no ABS light (knock on wood).

The resistance with the rear abs sensor was higher than the oem ford ones that I had, so I'm not even sure if that plays into anything or if that matters. I checked wiring and all seems to be fine. I will check out the wiring even more this weekend since I am going to be taking the truck apart a little bit to install a remote starter.

I'm hoping this is just a fluke for whatever reason.

On an unrelated topic, I will note that one time last year I had my right headlight not work for a day. I have a projector retrofit with hids and was going to work on it the following day. I go to start testing things the following day and it turned on no issues. Never had that issue again since. Still wondering wtf was going on with that...lol

I guess though in a way a 17 year old trucks wiring is going to eventually become brittle and problematic... :-(

-Nigel

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