Had this problem for a few years and I have lived with it, now I have had enough after a recent "close call". I have a couple of Superdutys and a couple of trailers so I have done a lot of dignostics. I have narrowed it down to the problem is in the truck.

2005 F350 with in dash factory brake controller. I have had the error messages of "trailer disconnected" and "TBC Fault". Like I said I lived with the messages and the annoying beeps, even pulled the fuse on occasion for a break from the beep.

Over the years I have had to increase the gain from 1.5 all the way to 10 to get the trailer to stop correctly with the truck. Yesterday I lost all braking at the pedal, gain at 10. The slide bar would activate the brakes with the pedal partially pushed.

I have replaced the rear pin connector and reground the ground on the frame next to the spare tire with no change.

I had the local dealer get me the pigtail wire adapter so I could disconnect my factory controller and plug in an aftermarket. I have the same problem with the aftermarket. I switched the trailer to another truck and all is fine.

My question to you guys is this, if the pressure switch in the master cylinder was bad would it cause the same problem with another controller? The aftermarket set up still gets its cue from the pressure switch. I thought about disconnecting that wire and going to the stop light switch like we used to with the old trucks but wasnt sure if that would create more issues

I give up and have had enough..... Any help appreciated.

 

I don't know much about the factory brake controllers, but I DO know that my aftermarket one (Tekonsha Prodigy P3) takes it's cue from the brake light switch on the brake pedal, not the pressure switch.

So, if the pressure switch DOES control the factory brake controller, I would think replacing it would cure the problem. However, most after market controller that I know of usually activate off the brake light switch.

 

Have you tried replacing the controller itself? I know that has cured the error messages problem for some people. There was a problem w/ water getting in the bumper connection and causing that problem, but if that's already been replaced, I think you're down to the master cylinder switch or the controller. Controller isn't cheap from the dealer but you might find one cheaper online somewhere. Shame to give up the seamless integration w/ the factory controller but that's been done too. Really doubt an aftermarket controller would have anything to do w/ the master cylinder but I can't answer that for sure. Does the aftermarket not work either? Did you unplug the factory controller?

I have the same TBC fault but the controller still works...I'm not happy to hear that it eventually totally fails. Maybe I need to move that higher up on my priority list.

 

The aftermarket controller was doing the same thing. From what I have read, based on my build date (late 2004) I have the earliest version and that Ford changed the controllers in early 2005. The dealer said $280.00.

I have no problem paying twice that if I can avoid what happened yesterday when I started to jacknife at a slow speed on a wet off ramp with a my mini excavator on my trailer (trailer and machine 12500lbs). Major pucker factor! I have been hauling tractor trailers and smaller equipment for 28 years and never thought I was in trouble as much as that.

I just want to remove the potential for replacing the master cylinder before I replace the controller.

Thanks to all for the info, I have solved many a repair on these forum boards. Some very educated people here and I like to here what others have had problems with, its a big help in diagnostics.

 

The built in brake controller uses the pressure sensor on the master cylinder to read the amount of brake pressure you are applying and it applies trailer brake power accordingly.

An aftermarket controller simply reads the brake pedal position switch via the brake light wire to tell if you are pressing the brakes at all. It then determines how much power to send to the trailer brakes based on an inertia sensor that tells it how much you are slowing down.

So... if you still have the problem with an aftermarket controller, the problem pretty much has to be in the wiring from the controller to the plug in the rear, or in the ground.

Generally these problems are caused by corrosion at the connector to the back of the 7-way, not in the 7-way itself. Remove that connection and see what it looks like. If it everything there is OK, go up the wiring harness to the connector above the spare tire and see what it looks like.

 

Wow, that doesn't sound fun. I'm thinking maybe I should fix mine sooner rather than later! One thing, you said it happened at slow speed - on the first generation of the controllers, like yours (and mine btw) they were set to not work at less than 15 or 20mph...don't ask me why. Could that be the problem in that situation?

Still doesn't explain why the aftermarket one doesn't work though - I'll defer to David on that one, sounds like he has you on the right track.

 

David,

You mentioned about the brake switch. My question is if I have the aftermarket (Activator II) plugged into the factory wire harness through a factory connector (factory TBC is disconnected from the harness and harness is plugged into the aftermarket controller), is the feed in from the truck coming from the pressure switch or the stop switch. If its the stop switch then the factory controller would be getting the same info..... I think

I tried going directly to the brake switch at the pedal and leaving the 4th wire in the factory plug behing the controller disconnected so its feed was directly from the brake switch but that didnt work either.

I dont have a wiring diagrahm so i used one of two wires at the switch that showed power when the pedal is pushed. I tried both and no luck.

The rear connection has been replaced and reground. You may be correct in chasing the wiring in between. I will check that today.

Thanks

Matt

 

No. You're not understanding what is going on.

On the master cylinder is a brake switch. It is just an on/off switch that sends a signal to disengage the cruise control when a certain amount of brake pressure is applied. It is a backup to the cruise control for the Brake Pedal Position switch in case it fails. That is all it does. Every truck has this switch.

When you have the integrated brake controller, there is also a SENSOR on the master cylinder that is attached to the brake controller to sense a range of pressure. All it does is provide the brake controller with how much pressure you are applying to the brakes. Trucks without the integrated brake controller do not have this sensor and the master cylinder doesn't even have a place for it.

On the brake pedal is the Brake Pedal Position switch. It controls the brake lights and sends a signal to the PCM to deactivate the cruise control, disengage the torque converter lock, etc. It also sends the signal to the connector for an aftermarket brake controller so that it knows you are pressing the brake.

At the rear, the rear connector is plugged into the wiring harness. This is the plug you need to check. Look at the back of the rear connector you will see a plug. Remove it and inspect it and it's wires.

 

Hi Matt,

I have been following along. Interesting problem. If I am following you, if you activate the red lead on the controller via brake pedal switch, you still get nothing to the pin for the brakes on the seven pin in the rear. Is that correct?

Steve

 

I get what your saying, The back of my factory controller has 2 connectors, what I will call the truck side and the harness side. I have disconnected the harness side and connected it to the aftermarket controller. Is the signal in that connector comming from the stop switch or the switch on the master cylinder?

 

The stop switch (Brake Pedal Position switch). The "switch" on the master cylinder isn't a switch, it's a variable resistor type pressure sensor. The aftermarket controller couldn't interpret it's signal.

 

Steve,

that is what correct, I jumped around the factory connector on that lead in an attempt to bypass the pressure switch.

 

David,

So It wouldnt matter to the Aftermarket controller. To be sure the aftermarket is getting the right signal where would I want to connect at the stop switch or should I leave it in the factory connection and head into the harness. I know the end of the harness is good so it must be somewhere in between

thanks

 

All you need to do is plug the aftermarket controller into the plug intended for it. The correct wires are all there for it. It might not hurt to use a test light and test out the wires. Check to make sure there is power and that there is power to the brake signal wire when you press the brake.

 

First of all, do not replace any more parts.

Controllers are very dumb animals. On your after-market controller, you have a black lead feeding 12-volt power off the battery, a white ground lead, and a blue lead carrying power to the rear. All a controlller is is a gated relay. If you activate the red, you should have power down the blue coming out, do you.

You need to know that first as the tells you whether you need to work before or after the controller. I always start by verifying my basic imputs. Remember, depending on the type of controller you still have to activate it manually, if it uses an accelerometer rather than a timed relay. You can even activate it without having brake pedal input as mightbehte case in an emergency.

Steve