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I'm gonna assume that you made a tester for the ITBC output (if you didn't, quit making excuses), SO...........

The Master Cylinder Pressure Sensor operates from a 5V reference generated within the EBCM. It also has a ground and an output.

Pin A (Ye/Bk tracer)....... Ground (referenced, not chassis)
Pin B (Gray)..................5 Volt reference
Pin C (Orange)..............Sensor output

With the pedal not depressed, key on, measure across B to A with a digital voltmeter. Voltage should be around 1 volt. Have a helper depress, slowly, the brake pedal all the way to full apply, and the voltage should rise to nearly 5 volts. Failure to change voltage will indicate a faulty sensor.


BTW, resistance between the blue and white wires on the trailer must be 2.0 Ohms or less. One magnet will not allow the system to operate under pedal braking BUT it will respond to the manual apply.
Mccall - what should the reading be for the output voltage at the bumper? If I use a multimeter, I get fluctuations at full output from 3 to 7 volts. I would think I should see at least 12 volts with the gain turned all the way up and the trolley brake maxed.

What does everyone else get?
 

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Mccall - what should the reading be for the output voltage at the bumper? If I use a multimeter, I get fluctuations at full output from 3 to 7 volts. I would think I should see at least 12 volts with the gain turned all the way up and the trolley brake maxed.

What does everyone else get?
The bottom part of your quote is the key to your lack of measurable output with no trailer connected if I understand your question right...

"BTW, resistance between the blue and white wires on the trailer must be 2.0 Ohms or less. One magnet will not allow the system to operate under pedal braking BUT it will respond to the manual apply."
 

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*TAG* for reading (otherwise I'll lose the thread lol..).
 

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Here is now the best price I've seen for the problem brake sensor (may as well keep it in your "wish list" in case it's needed:
 

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I think this really is what it says, 'Brake Fluid Level Sensor'. The needed part is the 'master cylinder brake pressure sensor', $78.74 shipped on Amazon. Check application before assuming if will fit your truck.
 

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Regardless the description, the GM part number is 15838718. Cured my trailer brake problem, going on two years now.
 

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I know this is an older thread but have been searching and found this test for the pressure switch.
When I test the switch I get 5v all the time, with or without the pedal depressed.
I have check the plug with a headlight and get nothing.
I do have the "service trailer brake system" message on every start up and the trailer brake don't work.
I'm assuming that the pressure switch is bad but want to check before I buy one.
BTW the price has come down, you can find them for under $40 now.
This is on a 2008 Silverado.

Thanks Bob
 

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Buy it. Easy replacement and easy fix to your problem. Doesn't get much easier than this.
 

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reviving this thread here for some input. I have the service trailer brake message on every start up. I checked the sensor and I see 5 volts when I turn the key on and the pedal is NOT pressed. I guess the sensor is bad no big deal under most circumstances a 50 dollar fix. However my bleeders on the front calipers are shot from the wonderful northeast so question is can this be bled from the senor port or am I looking at a new set of calipers?
 

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The instructions for replacing the brake pressure sensor specifically say to bleed the front brakes, and so does heymccall. So there is something there you need to pay attention to.

Having said that, if the fluid in the master cylinder is not allowed to drain out of the MC when the old switch is removed and new switch is replaced, It MAY be that you don't need to do the bleeding for the system to work. It's one thing if your ITBC doesn't work properly, quite a different, serious thing if your brakes don't work properly. Check carefully if you attempt to do this.
 

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Searched for ITBC problems but found a lot off stuff on SERVICE TRAILER BRAKE SYSTEM on the DIC but nothing on my problem of getting NOTHING on the DIC when I plug in my TANDEM AXLE trailer except perhaps a problem with brake pressure sensor, the problem seem to have started right after I had the dealer replace the lower left air inlet hose, just wondering if they could have messed something up.
 
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