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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15201
Experience:  GM Grand Master Technician 2007. 14 years experience.
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I am working on a 2008 3500 CCLB 4WD Diesel. I appear to be

Customer Question

Hi, I am working on a 2008 3500 CCLB 4WD Diesel.
JA: Are you fixing your 3500 yourself? What have you tried so far?
Customer: I appear to be having low voltage on my B+ signal going to the trailer brakes on a triple axle trailer with 12"x2" dextor axles and electric trailer brakes. The max voltage I see with the motor running and battery voltage at 14.+ is 11.44 when gain is set at 10. By moving the gain up and down I can vary the voltage. Shouldn't I be seeing the full system voltage?
JA: Have you tested the battery with a voltmeter? And can you see if it's leaking or not?
Customer: The ultimate problem and that the brakes don't seem to fully applied. I adjusted them all up to specsc. Cleaned the connections on the trailer pigtail and at the truck plug in. I have measured the current with a inductive pickup and it is putting out 15.5 amps total. With 5.3 to 5.4 going to each axle and each magnet 2.62 to 2.72. It used to stop great until the trailer pig tail got got and put it out of the truck socket and pulled the wires out of the junction box on the trailer and shorted out.
JA: Anything else you want the mechanic to know before I connect you?
Customer: I am wondering if I have damaged the TBCR in some way? Do I need to reset it? Do I need to disconnect both batteries to allow it to reset? So, the big question is what should the output from the TBCR be? Should it match the B+ voltage or should it be some voltage less?
Submitted: 10 months ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 10 months ago.

Hi there, I am Cam.
With your truck, the trailer B+ is not for the brakes, but for charging the battery on the trailer. The trailer brake blue wire will see a small voltage for self testing.
With that, do you have a brake issue on your trailer?
Do you get warnings on the dash of your truck? .

Customer: replied 10 months ago.
Sorry, I meant the blue wire for the trailer brakes. I have no warnings from the truck. The system seem to work fine except for poor brake engagment. The trailer is new with only 1200 miles on it and worked great until the trailer cable got pulled out of the junction box and shorted out wires while plugged into the truck.When the gain is set to 10 and display is reading all bars lit while either depressing the brake pedal or manually applying the brakes, what voltage should I see coming out?
Customer: replied 10 months ago.
Hello. Is anyone out there?
Expert:  GM Tech (Cam) replied 10 months ago.

Sorry I am also a Paramedic and unfortunately I was busy.

Have you tried a different trailer?

Customer: replied 10 months ago.
The problem follows the truck. I believe the output voltage from the relay is too low. What should it be under a setting of 10?