New GMC 2500 Wont Engage Trailer Brakes

Hey Ben, the P3 is a great unit, and I've used 4 different brake controllers, before having my current Ford IBC. All IBCs are not the same, and IMO, the Ford is top of heap.

To answer your question, my IBC manual lever is variable, from just a little, to locking the wheels. My IBC set on 5.5 of 10, will stop entire rig from towing speed, using manual lever, if I wanted, but no one wants heated trailer brakes, unnecessarily!

If you get a truck with IBC, especially a Ford, give the IBC a try Ben! Don't let old thinking hold you back! :)

Just don't ever throw away the P3!

Jerry

Most manual lever actuation will bypass the logic circuit (controller) and send power to the trailer brake wire, but am assuming they are all the same in logic.

My P3 also bypasses the logic circuit and sends power to the trailer brake wire

Question: are the OEM integrated brake controllers manual lever variable or just on/off in function ?

Also, my P3 (stolen and have to purchase another soon) leads the TV brakes. Even in a panic jab at the TV brake pedal.

Once power has been sent to the trailer wire by the P3, the accelerometer in the P3 takes over to proportion the power sent to the trailer wire.

Of course factored by the preset, but if the accelerometer senses building G forces, it will meter out up to full power to the brake wire.

Can and have stopped the whole setup without ever pushing the TV brake pedal far enough to developer MC PSI (not freeway, but it could and take longer with just trailer brakes…which will have the P3’s accelerator send ever more power once it senses whatever G forces vs preset). Try that with any highly integrated brake controller that uses MC PSI as the determining sense.

If one of these integrated trailer brake controls also has a brake pedal light switch sense, then it might likewise be able to stop the whole setup without ever developing MC PSI, but to date, have not read of that

Nothing wrong with OEM integrated brake controllers. Just not for me and if I do purchase another TV and it has a highly integrated brake controller…I’ll continue to go with a P3

Thermoguy wrote:
If it works with the manual slide, then the brakes work and the controller. The issue seems to be the foot actuation dealing with applying the brakes on your truck. I wonder if that is controlled by a computer or by some actual physical connection. They might have to replace one of those items.

Since the manual slide works, that means the integrated controller knows a trailer with brakes is connected and it can power the brakes.

On my 2015, the integrated controller works so well that I don't feel the typical feedback one gets from a aftermarket controller as the trailer brakes get applied. Feedback is very subtle till you do a very hard stop. And I did have one occasion where I had to do a 60mph panic stop when a merging car decided to stop in the traffic lane! Control was amazing, ABS on the truck was full on and the trailer stayed straight as an arrow.

As you stop if your in tow haul mode does the dash indicator for the trailer brakes show the trailer brake force and does it vary as you change braking force? If so I suspect it is working.

So GM has sent engineers out and they can't figure it out but maybe someone here can? Doesn't it have a factory brake controller?

Too many potentials for these 'highly integrated trailer brake controllers', but IMHO, it sounds like the MC PSI sensor is the main culprit in your case

It might need bleeding and/or replacement



Edit...be careful, too often they just give up and replace subsystems/components/etc. trying to 'fix' it...

And, too often, the root cause is still there, but now masked by those new components/sub-systems...

Guessing this won't be just a GM thing, but all OEMs now have 'highly integrated trailer brake systems'...

With a 2021 truck under warranty, demand Chevrolet fix it. Keep escalating up the chain of command.

If it works with the manual slide, then the brakes work and the controller. The issue seems to be the foot actuation dealing with applying the brakes on your truck. I wonder if that is controlled by a computer or by some actual physical connection. They might have to replace one of those items.

Find the fuses associated with the brake...I think there are 2. Take both out at the same time and reseat them. That will force the truck to reboot the brake controls. I have heard that has worked. Good Luck!!

Wow,certainly frustrating and something I've yet to hear of.
Perhaps cheaper in the long run to install an aftermarket brake controller.

Have you invested in a brake tool to verify pad spacing. Possibly the trailer and not the truck.

It will work with the manual slide