C1296 front left wheel speed sensor (Hill descent and ABS faults)

[FordFanStan]

I recently replaced all my brakes (calipers, hoses, pads, rotors) and installed RCV IWE eliminators on my 2010 with ~75k miles. After I got all of that done, I started getting the Hill Descent Control fault and ABS fault. I used my Xcal4 and it did not see any OBDII codes. I then used my Autel scan tool and found I was getting C1296-F0 front left wheel speed sensor code from the ABS control module. I found it odd the speed sensor would have failed as soon as I got everything back together and I inspected it, but I did not see any tears/cuts/frays, etc. I ordered a new one anyway, (Motorcraft #BRAB281) and installed it. Started it up, but it still had the faults. I then used the Autel scan tool to clear codes, removed the negative terminal for ~20-30 minutes, and started it back up. It was good for about 30 seconds and then everything faulted again.

I've read through numerous threads in the Gen1 and Gen2 sections regarding similar incidents. I checked all the fuses normally associated when these faults appear and the third brake light is dry with no condensation inside. Could the sensor not be reading due to the RCV IWE or too much grease inside or something? I don't know what else to check. Any help would greatly be appreciated as I know it would cost an arm and a leg with no warranty to take to a dealership for electrical diagnosis. Thank you in advance.

 

[B E N]

I don't think its an excess grease problem, those are just a hall effect sensor. Try running a continuity test from the harness at the sensor plug to the PCM, if possible have someone wiggle the wiring while you are ohming. It is possible something in the wiring got accidentally damaged while you were working. I believe one of the prongs is also power, I don't remember off hand what the voltage is, maybe @FordTechOne can shine light on the diagnostics.

Also make sure the sensor is fully seated, since it's magnetic the range of pickup falls off at an inverse square rate so a small distance makes a big difference.

 

[Dane]

Did you drive it after replacing the sensor or just start the truck? I had the same sensor go out on my 2012, but it was throwing a "Check Brake system" or something like that light, no actual CEL codes. I pulled the sensor out of an old wheel bearing I had kept (pull these sensors and keep them if you ever toss a wheel bearing!) and replaced the existing one. The existing one fell apart when I removed it, so I'm guessing that was part of the issue.. When I started the truck back up I still had the error, but it went away as soon as I started actually moving. It has been fine since.

 

[FordFanStan]

@B E N
I was hoping to maybe get a wiring diagram from the forum so I could perform such tests. I guess I could start by checking voltage at the connection, just to see if there’s something there.

@Dane
Yeah I moved the vehicle and the faults popped up. Since I have cleared the code/faults and everytime I start to move it is when it pops back on.

 

[FordTechOne]

If the DTC only sets when the truck is driven, it is most likely likely mechanical in nature, meaning sensor air gap or tone ring (internal to wheel bearing). Have you verified that the wheel speed sensor is mounted flush to the hub? Any rust/corrosion buildup at the sensor mount will increase the air gap, which affects sensor readings. If there are no issues with the sensor mounting, it’s possible that dirt/debris fell into the sensor hole during repairs. You may be able to use a flashlight and magnet to find/remove any contaminants.

 

[FordFanStan]

If the DTC only sets when the truck is driven, it is most likely likely mechanical in nature, meaning sensor air gap or tone ring (internal to wheel bearing). Have you verified that the wheel speed sensor is mounted flush to the hub? Any rust/corrosion buildup at the sensor mount will increase the air gap, which affects sensor readings. If there are no issues with the sensor mounting, it’s possible that dirt/debris fell into the sensor hole during repairs. You may be able to use a flashlight and magnet to find/remove any contaminants.

I finally got some time on a day off. I cleared the code and started truck and just let it run for several minutes while in park. No code.

Put transmission in R, D, P, several times shifting through gears slowly while not in motion with foot on brake. No code.

Drove walking speed holding brake slightly, up to a block in length. The speedometer needle was not moving at this speed. No code.

Drove without brake where speedometer needle started to move off the peg and boom, all dash lights were tripped and had the same left wheel sensor code trip.

Believing it is a mechanical issue at this point, I pulled the left front brake apart for like a sixth time. Nothing looked out of place, everything connected, seated, no real crazy dirt or rust to speak of. Pulled sensor and took pics, (1 and 2).

Then decided to pull right front brake apart to compare and everything looked the same. Took pics, (3 and 4).

 

[FordFanStan]

Is there something else I can test while it’s apart? Test for continuity or voltage or something?

 

[FordTechOne]

A few things...

• Is it the photo, or is the tip of the sensor damaged in the first photo?
• The mounting surface appears to have some rust/corrosion. I would wire brush that down to bare metal to ensure the air gap is correct.
• Is the tone ring in the second photo more centered in the sensor hole than in the first photo? It almost looks like the tone ring walked backward in the wheel bearing.

As far as electrical testing, you can't ohm check an Active wheel speed sensor. The fact that is only occurs when moving is an indication that it's mechanical. When the speedometer registers that the vehicle is moving, the ABS Module expects to see the same reading from the wheel speed sensors. When it doesn't, the DTC is set.

 

[CoronaRaptor]

A few things...

• Is it the photo, or is the tip of the sensor damaged in the first photo?
• The mounting surface appears to have some rust/corrosion. I would wire brush that down to bare metal to ensure the air gap is correct.
• Is the tone ring in the second photo more centered in the sensor hole than in the first photo? It almost looks like the tone ring walked backward in the wheel bearing.

As far as electrical testing, you can't ohm check an Active wheel speed sensor. The fact that is only occurs when moving is an indication that it's mechanical. When the speedometer registers that the vehicle is moving, the ABS Module expects to see the same reading from the wheel speed sensors. When it doesn't, the DTC is set.

I always feel smarter when I read your posts!

 

[FordFanStan]

• Is it the photo, or is the tip of the sensor damaged in the first photo?
• The mounting surface appears to have some rust/corrosion. I would wire brush that down to bare metal to ensure the air gap is correct.
• Is the tone ring in the second photo more centered in the sensor hole than in the first photo? It almost looks like the tone ring walked backward in the wheel bearing.

1. Just the pic/little bit of grease on the tip. This is the brand new sensor I installed. I wiped that off and there are no visible defects with the old or new sensors.
2. I cleaned everything off to bare metal (see pic), however remember this first tripped after I replaced the IWE and brakes, but did not remove the sensor until I replaced it with the new one.
3. I can fit calipers in the hole, but stuck a flat blade screwdriver in the hole to measure and by eyeball, it looks even with the pass side.

I suppose I could Jack up the rear of the truck too, and then accelerate in 4wd without having to reinstall everything to test if it’s working?!?