A buddy of mine has a 2005 f-350 crew cab with a 6.0 auto trans 4x4 and his cruise has started acting up. The cruise works fine but when he hits his brakes it does not shut off. His brake lights are working fine and no other problems. Does anybody have a clue as to what this could be?

 

There is a switch on the master cylinder that is supposed to cut out the cruise control.

Sounds like it's shorted or corroded or something.

Pull the connector from the switch, and with a DVM/ohm-meter, check for continuity. You SHOULD get continuity in the switch when you don't press on the pedal and the switch should show an open when you ARE pressing on the pedal. If not, the switch is bad.

 

I just went through this problem. There are TWO switches that will disengage the cruise control.

The brake pedal position switch, which is on the connection between the brake pedal lever and the rod that pushes the master cylinder, is supposed to provide this function. If it fails, then the pressure switch on the master cylinder is supposed to act as a backup.

What I found is that at times I'd lightly touch my brake pedal and the cruise wouldn't disengage like it normally did. I'd have to brake harder (pretty hard actually), to get the pressure switch to do it.

I replaced the brake pedal position switch and it works fine now.

Also, the BPP is two switches in one, technically a double pole switch. One pole operates the brake light and the other pole signals the PCM to do things like disengage the cruise, unlock the torque converter, stop the high idle if it's on, etc. So even if the brake lights are working, the BPP switch can be bad.

The Ford part # is F87Z13480AA. I got it at a very good price and shipped quickly from http://www.ftepartsguy.com/

 

Oh, and on second thought. If your friends cruise won't disengage AT ALL even with fairly significant braking, then the master cylinder pressure switch is probably bad also and I'd follow Krewat's advice above as well as replacing the BPP.

 

Thanks David, didn't even think about the brake pedal switch - good point.

 

Thanks for the help, I will pass it on to him and see what happens. Today he said the cruise was working fine but now is ATC had quit working for a while..go figure.

 

I know this is a stupid question and im an idiot for asking, but what happens in a situation like that. If you were to try to stop really quickly and the cruise didnt disengage wouldnt you do alot of damage?

 

Mine was intermittent at first. It would be fine for awhile, then it would act up for awhile. Eventually it quit working right altogether.

 

I guess that's why there's both the brake switch, AND the pressure switch on the master cylinder.

Then, there's always the "off" button on the steering wheel

 

Foot off the gas and on brake means engine is at idle and the pedal hydraulic brake will stop the truck. Granted there will be groaning of parts but it will stop. The driver will .

But in this case the stop light switch on the brake IS defective and possibly the hydraulic back up. Change both or don't use the cruise.

 

The cruise will definitely try to push down on the go-pedal, it won't be at "idle".

I do, however, think the PCM has enough "brains" to figure out that something is wrong once it hits WOT and it'll shut cruise off on it's own.

 

I can tell you that when you hit the brakes and the cruise doesn't disengage, there is a significant "pucker" effect. As to how much damage it will cause? I guess it depends on what you hit.

I can't say I really know for sure, but I kind of doubt that the brakes will stop a truck at highway speed with the cruise on. Hopefully if anyone were to find themselves in that situation, they'd have the presence of mind to hit the off button, and if that didn't work turn the key off.

 

You are right I forgot the cruise would hold the throttle, but warning turning the key off will kill power steering and power breaking. If you turn it off the cruise will disengage, but you must immediately turn it back on. Putting the truck in neutral will cause the engine to redline and hopefully it will stay together, the computer to hold the rpm's and allow the time to turn the key off without locking the steering wheel then back on. In any case this would be a really bad position to be. Guess you could aim for the snow bank but a little difficult down here in the south with no snow.

 

Help! Driving cross country last night in 2001 Expedition. Recall has been done. 80 mph highway driving. Cruise control would not disengage when the off button was pushed or when brakes were hit. Ended up slowing with great break pressure. Turned off truck. Started again and engine raced so turned off. Started again and immediately put in gear. Cruise indicated it was off. Light on dash was off. Cruise released after a bit. Decided not to use cruise any more. Got back on the highway.

About an hour later - without turning on Cruise control and with no dasboard light indicating it was on, the Cruise took over again and put me at 80 mph again and increasing. Had to pull off at high rate of speed on a ramp with full pressure on brakes. Turned engine off at 40 mph and manhandled steering and brakes into a truck stop. Was going to try to disengage cruse from throttle lever but decided instead to separate the fuse connector to the brake release switch. That seemed to neutralize the Cruise control. Drove the reste of the five hours home without incident.

Dropped it at shop this morning. Naturally, unable to make it repeat. The fact that it started on it's own made me think the stearing wheel switch might be bad, but if it started on it's own, wouldn't the dashboard light indicate it was on? I want to get an idea of what might be wrong so the shop doesn't just replace everything and charge me a small fortune.

All ideas and comments appreciated. Thanks!

 

Wrong forum, this is the Super Duty section.