Brake idiot light on dash.

[F350camper]

Hey guys, just recently in really cold weather (10° and below), my brake idiot light will come on some times. It only happens when I’m waiting a stop light angled up hill. Then when I get back on level ground it goes off. Usually doesnt come back for a few days.

The reservoir is full, and the ebrake is off. Anything to worry about? Any ideas what's causing it?

 

[Warwagon]

Rob,
My van does that occasionally too. Never lasts that long. If I rev it a bit while sitting, or drive it, the light goes out. I'd bet that the vacuum lines from the pump up to the vac manifold and possibly some others are getting dried out and stiff with age. When it gets cold, something in the system (probably a plastic nipple) contracts enough to cause a small vacuum leak. I MAY try to dose all of the rubber hose ends I can see with a drop or two of oil to rejuvinate them (this trick works well on old Johnson/Evinrude twin-line fuel hoses that have been left sit for years between uses). I'd hate to have to try to find replacements for all of those various sized hoses though.
Mark

 

[F350camper]

ohhh, so it'll come on for vacuum leaks/ too little vacuum at the booster? I didn't know that. See there, been on the new site less than a week, and I already learned something.


That’s cool, maybe I’ll give it a look-see the next time I’m in there.

 

[JPR]

Three things will cause the light. Brake fluid level in the master cylinder, too low of vacuum, pressure mismatch between front and rear brakes.

Here is the vacuum test part one and part two

 

[argve]

Rob,

The low vacuum warning switch is located on the passengers side fender well about where you located your splash pump. It's a tuna can looking thing with wires and a hose coming off it. Check to see that the electrical connections are good as well.

 

[F350camper]

Good deal!
Thanks agian Mark, Jon, and Travis