ITBC

dmaxing wrote:
Has anyone heard that if your brake pressure sensor is bad your ITBC might not work?

Yes, if the pressure transducer fails, ITBC stops working. Mine did exactly that, but when it did so, the DIC said "service trailer brakes" or something similar.

Michelle.S wrote:
OK, the quote above is from my post. Ran into that problem when our interface box failed (installed infront of our Hydraulic pump for the disc brakes to make GMs think they are connected to Electric Drum brakes).
Using an Ohm meter, measure the resistance on the trailer pig tail between the brake term and the ground term. This resistance needs to be approx 3 ohms for the GM computer to acknowledge that a trailer is connected.

I'm going to assume that the controller looks for a resistance of less than 3 ohms.

according to a table from dexter axles, each magnet on an electric brake is around 3 ohms. So even on a dual axle trailer with 14 ga wire for the brakes, should be around 1.5ohms plus any wiring resistance, 50 ft of #14 wire is around 0.2ohms. So even a tandem axles will be well under the 3 ohms upper limit.

So there should be plenty of margin for the IBC to see a trailer connected if the trailer wiring and brakes are working as expected.

In a way this is much better than an aftermarket controller that just sends a voltage down the line. If there is a bad connection in the line, the controller doesn't do squat and you don't know that until it is to late and you notice the brakes aren't working as expected.

I do know on the GM controller if you unplug the connector with the ignition on it will give an error message. I assume that would also happen if you develop a high resistance, broken wire etc. while driving.

I also suspect that by the way it alarms, if you hook it up with greater than around 3 ohms and less an infinite resistance (open ciruit) to the brakes it will alarm. the circuit will detect a load, but greater than 3 ohms, and will alarm.

To the OP, measure the resistance to the brakes on the trailer. on a tandem axle it should be less than 1 ohm total by the dexter chart. (need a decent meter that can null out lead resistance, or short the leads and subtract that number from the reading you get when measuring the brakes).

If it is over 3 ohms, there is something not up to par, that's for sure.

OK, the quote above is from my post. Ran into that problem when our interface box failed (installed infront of our Hydraulic pump for the disc brakes to make GMs think they are connected to Electric Drum brakes).
Using an Ohm meter, measure the resistance on the trailer pig tail between the brake term and the ground term. This resistance needs to be approx 3 ohms for the GM computer to acknowledge that a trailer is connected.

dmaxing wrote:

Miles Away wrote:
I have found that most vehicle dealers have little or no clue about diagnosing issues with OEM brake controllers. You may have to go to a trailer dealer, NOT necessarily an RV dealer, who will have the right equipment and knowledge to diagnose the problem. Just to eliminate a problem with your truck or trailer, hook your truck up to someone else's trailer and see if it works. If it doesn't then you can be sure the problem is in the truck. Are all the other pins working (lights etc)? Are you getting juice to the brake pin at the rear of the truck?

I am getting a pulsing power on the brake controller pin.

If your looking at the 7 pin connector and NO trailer connected, that is what you should see on the GM IBC from what I've read about the IBC. My understanding is it sends a low voltage pulse down the connector to determine when it actually is hooked to a brake system.

Here is a quote on how the IBC operates

OK, here's the story on GMs. The installed Brake controller send a digital signal down the line (approx 3 to 4 volts) looking for the correct resistance. Once it see the correct resistance it will give the "Trailer Connected" message and will now supply the proper voltage and current to the brakes. What happens these "So called Techs" put a voltmeter on the brake control line and read that digital signal and tell you there is a problem with the controller which is untrue.

If it is pulsing when the trailer is connected, then it may be not working correctly.

Miles Away wrote:
I have found that most vehicle dealers have little or no clue about diagnosing issues with OEM brake controllers. You may have to go to a trailer dealer, NOT necessarily an RV dealer, who will have the right equipment and knowledge to diagnose the problem. Just to eliminate a problem with your truck or trailer, hook your truck up to someone else's trailer and see if it works. If it doesn't then you can be sure the problem is in the truck. Are all the other pins working (lights etc)? Are you getting juice to the brake pin at the rear of the truck?

I am getting a pulsing power on the brake controller pin.

Just to evaluate all scenarios, I would hook up another trailer to ensure the issue is with the controller. Then you have a solid argument.

Go to a different dealer.

I have found that most vehicle dealers have little or no clue about diagnosing issues with OEM brake controllers. You may have to go to a trailer dealer, NOT necessarily an RV dealer, who will have the right equipment and knowledge to diagnose the problem. Just to eliminate a problem with your truck or trailer, hook your truck up to someone else's trailer and see if it works. If it doesn't then you can be sure the problem is in the truck. Are all the other pins working (lights etc)? Are you getting juice to the brake pin at the rear of the truck?