Check Brake System Warning

[Michael Edwards]

So I'm really not naive, and realize there are probably threads about this already. And if your simple response to this is a link to a previous thread, I thank you. But he we go...2012 SCREW 112,000 miles bought used first of Dec 2020...second owner as far as I can tell by the Carfax....

I have the "check brake system" warning light coming on randomly. It seems to only come on when I reach speeds about 65 mph. Never comes on just puttsing around town, usually rolling down the interstate. System sends out a warning tone and the check brake system light comes on and stays on. But when I stop and turn off the truck, the light goes off, and does not come back on until I reach the higher speeds again. Every time, not once has is been on after turning the truck off.

So...ideas???

sensor? booster? vacuum leak?

Thanks in advance

 

[MTF]

You should try to look for a code from an OBDII reader.
There are quite a few things it could be.

Wheel speed sensors come to mind right away but who knows.

E-brake switch
Brake fluid level sensor
Come to mind.
I'm grasping at straws here, I'm sure someone will chime in with better ideas.

 

[Don S]

Your brake booster has two ports, rather than the typical one on older vehicles. The upper port has the main vacuum line attached. The lower one has a sensor attached. Both use an o-ring to seal the connection into the booster.

I had to add a second line to the lower sensor unit to operate the brakes when I tow my Raptor behind my motor home. I had to remove the sensor and plug a "Y" adapter in that held the sensor and ran a second vacuum line to a braking system. When I put in the adapter, REALLY tight fit, I tore the o-ring that fits in the booster. I didn't realize it at first. After that, I started having the same issue as you. Over 65 on the freeway and not every time, the light would come on. I would stop and restart and it would go out and then come back days later. Once I replaced that o-ring, a few dollars at Ford, problem solved.

 

[B E N]

What sort of condition is the brake system in? Has it ever had the fluid replaced? Are the Pads, rotors, calipers, master, abs block all stock stuff?

 

[BenBB]

Well...didya check the brake system? J/K but @Don S o-ring is a good start, have you ever had issues or leak at third brake light? I think it can cause ABS issues, not sure about the message you’re getting. OBD2 scan might help...

 

[COBRA90GT]

Fluid level checked out OK under the hood ?

 

[GitErDunn]

I had that come up awhile ago randomly as I was highway driving... Just recently did a complete fluid flush of everything front to back... Everything checked out visually and wasn't acting weird, cleared the code and it has not come back and been no problems in regards to acting weird etc still...