Brake assist failure

[08navigator]

My wife drives our 2015 extended length navigator. It currently has 49k miles on it. We've been experiencing a rock hard brake pedal after the truck sits for a few hours. No other issues have pooped up with the brakes until yesterday.

My wife had driven 30 miles on the highway, pulled into our subdivision and was doing 20mph going down the hill. A dump truck was approaching so she hit the brakes to slow down and the pedal was rock hard. Tons of brake system lights lit up the dash. She said she could barely apply enough force to slowdown at all(110lbs and 7 months pregnant). She pulled into our driveway shortly after with the brakes acting the same way. She shut the suv off and then restarted and the brakes began acting normal. The brake fluid looks normal and is at the correct level, the pads are still on good shapeI drove it to work (55 miles) today and the brake worked great.

What can I do here? We have the 6 year 100k bumper to bumper warranty through Lincoln/Ford but with the brakes not currently acting up, will they do anything? Does the brake failure log itself in the system to where they can see it? I obviously need to do what I can to make sure this doesn't happen again.

I will say we had some bad weather when this happened. It was rainy and cold(33ish degrees). She did not slide or anything like that. Just a light pedal push.

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[stewartsoda]

If the lights lit up on the dash there may be codes you could see with a code reader.

 

[99WhiteC5Coupe]

I own a 2015 Ford Expedition Limited 4x4, purchased new.

There have been several posts on this form regarding the problem you describe on 2015 models (mostly Expeditions).

I do not have the posts bookmarked, but its seems the problem was with some type of seal between the vacuum booster and the master cylinder. I recall the posts because I have a 2015, and have had a variety of defects (but not what you describe).

I would NOT drive the vehicle, but have it towed to the dealer for diagnosis and repair. There MAY be some type of service information or TSB that the dealer would have access to.

Good luck - let us know what you determine.

 

[Frank Wilson]

Is it possible abs was activating. Im glad the two of them are safe.

 

[08navigator]

Is it possible abs was activating. Im glad the two of them are safe.

if so, It stayed activated after that. She drove the rest of the way home, pulled in the driveway, sat for a few minutes and then pulled in the garage. The whole time it was like that.

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[bobmbx]

Sounds like your brake booster is failing, although the cause is unimportant for now. What is important is that your car is not safe to drive. I agree with 99WhiteC5Coupe. Have it towed to a shop.

 

[762mm]

Sounds like your brake booster is failing, although the cause is unimportant for now. What is important is that your car is not safe to drive. I agree with 99WhiteC5Coupe. Have it towed to a shop.

I would concur on this. The brake booster is failing or there might be an external vacuum leak, however the latter is unlikely since the problem is intermittent.

It sure as heck sounds like an internal brake booster vacuum valve or seal not sitting properly, perhaps... since the reservoir cannot build / hold pressure, but only sometimes.

 

[Trainmaster]

If no problem can be found, I'd probably replace the booster and check valve.

 

[Frank Wilson]

if so, It stayed activated after that. She drove the rest of the way home, pulled in the driveway, sat for a few minutes and then pulled in the garage. The whole time it was like that.

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Oops , i missed that part about is staying that way. So probably not abs

 

[08navigator]

Update:. The dealer was able to find the brake failure code stored in the system. They weren't sure what caused it but did say my driver side iwe hose was not attached(a different dealer replaced my iwe's and hubs about 5k miles ago). I'm not sure if this happened recently or not. We have only driven it on pavement so I found that odd.

The dealership replaced the brake booster as a just in case fix. Unfortunately, our brake pedal is still getting hard while sitting overnight so I do think we still have a vacuum leak somewhere. Hopefully we do not have a brake failure again with the new brake booster.

Sidenote:. They replaced the running board hinges and motor to the tune of $1550(covered under warranty). That is an insane price for a feature that is so stupid.

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