New GMC 2500 Wont Engage Trailer Brakes

[Paroled]

I have a new 2021 GMC 2500, Diesel. It will not engage trailer brakes unless the brake pedal is mashed to the floor. It is this way on any trailer it’s hooked up to. My 04 Silverado works fine on my trailer. Dealership could not diagnose. Opened case with GMC and they have sent engineers twice and no luck. Anyone hooked up an aftermarket brake controller to a new GM This has been going on for 7 months

[Paroled]

GM Engineer was supposed to come to the dealership Thursday for the third time and they canceled and told me I needed a Cam adaptor for the IBC to work with my new Montana Fifth Wheel. I informed them they are installed from the factory and my coach has one. He evidently hadn’t talked to the other engineers or dealership because the truck works on no trailers and they know that. GM Customer service called today a I told them I want a new truck. I have reservations in Florida the end if the month. Not looking good.....

[p220sigman]

I agree that I wouldn't have taken it back from them with the , "Sorry, can't figure it out and fix it" decision. With you taking it back, the time you have it with the brake issue still going likely isn't counting towards the time it is down for repairs under most lemon laws.

[mkirsch]

Okay, I got less lazy and did a quick google. Here's a website that explains California lemon law:

https://www.lemonlaw.com/california-lemon-law.html

[mkirsch]

I agree. This is a warranty issue, a safety issue, a liability issue. Don't let them off the hook.

Heck I would not have taken the truck back when they said "can't fix it." I would say keep it until you fix it and give me a loaner in the meantime.

Maybe this is a myth and I'm too lazy to go look it up, but I think they're on strike two of the three strikes that the lemon law allows. If you bring the concern to them once more and they are unable/refuse to fix it, you've got a case.

Even these "highly integrated brake controllers" use an accelerometer to sense the deceleration of the vehicle and apply trailer brakes to match. It sounds to me like this part is faulty in your new truck.

[Me_Again]

The engineer that redesigned the RAM IBC in 2015(maybe it was 2014) must have moved to GM. RAM had a good IBC however most users in around 2015 started complaining about these pulse width controllers verses older current varied ones. RAM's decreased braking as the vehicle slowed. I found running mine in Heavy Electric over hydraulic on my drum brake trailer worked better.

[BenK]

MFL...Thanks for you comments and yup, at 73 and am older than most on this forum, but control logic isn't much different from when was designing controllers decades ago.

Yes, lots of the components are faster, more sensitive, and CHEAPER nowadays, but the logic/truth tables are about the same...albeit with many more variables tossed into the fray by having to integrate with everything.

Why know that some of these issues are founded in the time-outs designed into the logic tables. Also question how 'real-time' these OEM's software is and that is part of the time-outs know is happening in a real-time environment

So which did the designers/architects decide should have a higher order flag? The ABS? The traction control? The IBC? "Real-time" meaning that the computer deals with a high order flag before doing anything in the queue. 1st, 2nd, 3rd, etc flags are dealt with in that order. Then within 1st order flags, there are other hierarchical levels

Akin to the age-old relay race issues of my day.

IMHO, too close to a Rube Goldberg these IBC's. Simplicity of a separate controller appeals to me. If it flakes out, replacement is around $150 bucks and is a plug and play. Vs IBC requiring an engineer to diag properly with tooling that costs in the tens of thousand of bucks. Even then, they resort to replace & cross fingers it works.

IMHO, most folks who didn't like their P2/P3 didn't have them setup well and/or their TV's brake pedal switch isn't as sensitive as GM's, which only takes about <0.03" movement to 'click' on the TV's brake circuit.

Bottom line: found some rust on the roof of my 1996 Suburban, right next to the top windshield edge. Must have had something hit it & compromised the paint/galvanized coating. That might cost more than I'll wish to...but stuck wanting to build a HO 7.4L (miss the C2/L88). Stuff has been chipping away at that, as found out that GearVendors does NOT fit in a 1996 4x4 Suburban because the tranny tail housing is gone & replaced by the Xfr case.

[Grit_dog]

OP, of course you can spend the time and money and get an aftermarket controller. It’s the easy thing to do if you’re the type who is afraid of confrontation.
Otherwise, it appears you have a lemon law case ripe for the picking or continue to demand it be repaired.
You have a bigger hammer in your hand than you think. You have a “safety” issue that is unresolved by a billion dollar company and their “defective” product.
Use all the ammo in your bin brotha. Don’t puss out and give in!

[Grit_dog]

BenK wrote:
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

I sometimes have to lol at statements like the last one! Such conviction!

[aftermath]

Paroled, I have been where you are and I feel for you. Since the GMC crowd say their controlers are very good, I would fight with the company for a solution. You can even ask for a new truck if it gets to that point.

That said, I had a P2 controller on my first Tundra and it was great. I moved up(?) to a 2017 Tundra with a built in controller and it was terrible. It was a timed controller and after meeting with Toyota, writing letters and making phone calls they told me it had been tested and that it was performing to standards which was all true. I still had my controller, found an in dash bracket and You Tube video and installed it myself. It is still working and working well.

[ktmrfs]

BenK wrote:
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

I had a P3 on my 2004 silverado. IMHO the GM IBC on our 2015 Denali is light years ahead and orders of magnitude better than the P3.
smoother, quicker acting, better modulation

As I mentioned in an earlier post I had to do a panic stop from 60mph ABS on full, truck and trailer stayed absolutely straight and trailer braking compared to the P3 was way better.

[MFL]

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

[BenK]

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

[ktmrfs]

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.

[LITEPHIL]

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?