Check brake system message

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rvtrcr

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2011 supercrew, 77k miles - been getting a constant "check brake system" message for quite a while now. Here's what I know - I've changed front hubs, front wheel speed sensors and IWE's , all vacuum lines from booster to IWEs - including solenoid that controls them. I've smoke tested all that as well and no leaks. Forscan says low vacuum - thats it. Nothing about wheel speed sensors. I've cleared DTC's and the low vacuum comes back. Every now and then it acts like the ABS is engaged when backing up at parking lot speeds - also happens moving forward - get to about 10 mph and it goes away. It's not low on brake fluid... Anyone?
 

The Car Stereo Company

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2011 supercrew, 77k miles - been getting a constant "check brake system" message for quite a while now. Here's what I know - I've changed front hubs, front wheel speed sensors and IWE's , all vacuum lines from booster to IWEs - including solenoid that controls them. I've smoke tested all that as well and no leaks. Forscan says low vacuum - thats it. Nothing about wheel speed sensors. I've cleared DTC's and the low vacuum comes back. Every now and then it acts like the ABS is engaged when backing up at parking lot speeds - also happens moving forward - get to about 10 mph and it goes away. It's not low on brake fluid... Anyone?
most likely your e brake. i broke my e brake a few years ago. but first the sensor went bad and kept dinging at me so i disconnected the wire from the ebrake. i was running trails in texas at the time, bugged the crap out of me. im guessing your e brake sensor is bad.
 

FordTechOne

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You have one of a few possible issues occurring - A biased brake vacuum sensor that is reading artificially low, a vacuum leak, a leaking booster check valve, or a failed booster.

The ABS monitors vacuum at the brake booster to ensure sufficient vacuum in available for full brake assist. If the sensor reports low battery vacuum, the ABS module will run the hydraulic pump motor in the HCU to provide supplemental brake assist. This is why it feels like your ABS is activating at low speeds; it’s providing additional hydraulic pressure.

I would recommend verifying the actual vacuum available at the brake booster first. At hot idle, it should be approximately 17-20 in-hg. If it’s low, you have an engine performance issue (unlikely) or there is still a leak somewhere. Cap off vacuum lines until you find the source of the leak.

If sufficient vacuum in available, suspect a leaking booster check valve. When you accelerate, engine vacuum drops. The check valve is there to prevent vacuum in the booster from depleting. You should only be able to blow air through the check valve in one direction; otherwise is is faulty.
 

The Car Stereo Company

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You have one of a few possible issues occurring - A biased brake vacuum sensor that is reading artificially low, a vacuum leak, a leaking booster check valve, or a failed booster.

The ABS monitors vacuum at the brake booster to ensure sufficient vacuum in available for full brake assist. If the sensor reports low battery vacuum, the ABS module will run the hydraulic pump motor in the HCU to provide supplemental brake assist. This is why it feels like your ABS is activating at low speeds; it’s providing additional hydraulic pressure.

I would recommend verifying the actual vacuum available at the brake booster first. At hot idle, it should be approximately 17-20 in-hg. If it’s low, you have an engine performance issue (unlikely) or there is still a leak somewhere. Cap off vacuum lines until you find the source of the leak.

If sufficient vacuum in available, suspect a leaking booster check valve. When you accelerate, engine vacuum drops. The check valve is there to prevent vacuum in the booster from depleting. You should only be able to blow air through the check valve in one direction; otherwise is is faulty.
duh.... i somehow skipped over the part where he said "vacuum"

it was a long day yesterday.
 
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