Brake service light comes on while cruise control activated

[tgams]

went on a trip today, and while cruising down the interstate about 75, the service brake light came on. If I de-activate the cruise control it goes away.. any idea why? Brakes seem to work perfectly, not down on fluid. Never came on before at all. 2010 expy xlt, 120000 miles

 

[bobmbx]

I'm gonna date myself here....nobody laugh, got it?

Does your cruise control use the vacuum system? If so, a leak in the vacuum tubing to the CC controller/actuator can affect the vacuum booster, causing the brake service light to activate.

At least, in the old days that could happen.

 

[Trainmaster]

Yeah, you dated yourself there. It's all electronic now with a motor controlling the throttle plate.

 

[tgams]

I thought about a vacuum leak, looked at all the hoses and stuff around the brake booster /master cylinder it’s the strangest thing, thinking it might be in the speed sensor or a relay problem, but I guess I need a decent schematic....

 

[Plati]

Yeah, you dated yourself there. It's all electronic now with a motor controlling the throttle plate.

I thought on newer vehicles .. brakes were also used in cruise control & traction control, etc?

 

[Michael Shepherd]

Adaptive cruise requires the brakes in order to maintain following gap/distance.

 

[tgams]

Does this truck brake automatically in cruise?

 

[mquick5]

Adaptive cruise requires the brakes in order to maintain following gap/distance.

I didn't think the 3rd gen had adaptive cruise? My 17 either dont have it or it dont work, idk.

Sent from my SM-G930T using Tapatalk

 

[tgams]

does anyone else have any ideas? On the way home Thursday I tried it again, activated cruise control...came on and maintained speed fine...after about five minutes in cruise, the service brake system light came on and the message center indicated service brakes..I turned cruise off, and about 30 seconds afterward the light went off, and the message went away. This happened twice in a row, then i just left cruise off and the indication never came back. When I got home i scanned the computer for codes and found none.

 

[tgams]

anybody?

 

[99WhiteC5Coupe]

does anyone else have any ideas? On the way home Thursday I tried it again, activated cruise control...came on and maintained speed fine...after about five minutes in cruise, the service brake system light came on and the message center indicated service brakes..I turned cruise off, and about 30 seconds afterward the light went off, and the message went away. This happened twice in a row, then i just left cruise off and the indication never came back. When I got home i scanned the computer for codes and found none.

You say you scanned but no codes. Some scanners cannot retrieve certain codes, such as the air bag system and other systems.

Do you have a high-end scanner?

Perhaps you may have to take the vehicle to a Ford dealer to have the system scanned for any fault codes?

 

[Cyclone]

Not ignoring you, I just don't have an answer.

 

[Trainmaster]

I can make guesses but they would be just that. Current leakage in the brake light switch? I would wait for matters to get worse or, as 99White said, search for a code when the light's on with a better scanner that reads the special Ford chassis and ABS codes. I use an AutoEnginuity scanner.

 

[chuck s]

It may be a brake problem. My '17 feels like it brakes in Cruise to control speeds in downhill situations. Down shifts for sure on down grades. The '07 never felt this way and just coasted.

No adaptive Cruise in these cars (my wife's Subaru will maintain vehicle spacing including hard braking so I know how that feels).

-- Chuck

 

[Flexpedition]

If your truck is 4X4, make sure the selector is switched to 2WD mode and not auto. If your truck isn't 4X4, proceed regardless.

With the truck running & in drive, immediately to the left of the 4-way flasher button is advance trac traction control. Press it one time and release, you should see the icon burning steady in the message center between gauges. Now press it again and hold down for about 5-7 seconds until you see that icon flashing in the message center.

Drive up to 30MPH and turn on and set cruise control. If brake light does NOT illuminate, you'll want to get a better quality scanner as suggested, one that can diagnose Control Trac. Chances are there is an issue with a tone ring or reader at one of the 4 wheels.

 

[tgams]

thank you so much everybody for all the responses..i guess i'll have to take her to ford one of these days and see if they can pic a code..it hasn't happened in a while, so i was thinking it might be brake dust on one of the sensors, but it would be nice to see if there is a code...thanks again, and i'll update once i get a chance to have it checked.

 

[tgams]

BTW, it's a two wheel drive...it was a police vehicle before i got her i do believe, a k-9 due to all the dog hair that was in her.