Levitation
Well-known member
- Joined
- Aug 12, 2009
- Messages
- 1,300
- Fluid Motion Model
- C-248 C
- Hull Identification Number
- fmlt2510f809
- Vessel Name
- Charlotte Ann
My trailer and truck have been together since both were new. The GM trailer brake controller (ITBC) has always recognized the trailer being plugged in and controlled the trailer braking properly. With no warning signs it refused to recognize the trailer when plugged in (January) and therefore I had no trailer brakes from Michigan to Florida this year..
1. Took the trailer and truck to a trailer repair place. They went through the Brake Rite system and declared it working properly on their test box.
2. They applied the test box to the truck and declared the truck's brake controller was working.
3. Plug the trailer into the truck and no joy.
4. Plugged the trailer into another GM truck and no joy.
5. Talked to Brake Rite and he gave me the secret test procedure for testing his brake controller and pump. It passes with flying colors.
7. Went back to the trailer repair place and discussed at length. He finally told me I am the third truck he has seen that has problems with the GM ITBC recognizing electric over hydraulic trailer brake systems. It apparently works fine with electric solenoid brakes. He solved the other two customers problem by disabling the GM ITBC and installing an aftermarket controller. That rubs the fur on my check book the wrong way and I declined his "fix".
6. Talked to the local GM dealer and he says he is aware that the GM ITBC has problems with electric over hydraulic trailer brakes. He says GM has not put out any service bulletin on how to deal with this problem and declined to 'work' on the truck.
7. Spent considerable time on the internet researching the problem and it is indeed a problem. Noted in a couple of reports their controller works fine with electric brakes (solenoids) but not with electric over hydraulic. Thought about the difference between the electric brakes (solenoid) and electric over hydraulic and decided the ITBC senses or pings the brake control line (blue) for the presence of the solenoid windings.
8. Measured the input resistance of the Brake Rite controller and got roughly 160 ohms. Found an electric brake trailer out in the storage lot and measured the input resistance of the braking wire and got roughly 0.2 ohms (almost a dead short). Put on my thinking cap and decided if I shorted the brake control wire on the truck bumper (blue) to ground (white) it would trick the ITBC into thinking there was a trailer plugged in. So I did. The ITBC sneered and said "check your trailer wiring buddy", and proceeded to ignore me otherwise. I was a bit put out by the 'sneer' in the glowing message, but I had learned something. The ITBC does indeed check the resistance (impedance) of the brake control line to see if a trailer with brakes is plugged in. An open circuit is no trailer brake and something less than a short is a 'brake' being present. So how much less than a short is needed?
9. Went to Wally World and got a trailer side marker light with a bulb and waltzed back to the marina doing the macarena across the lot because I am sooo smart. Jumped the bulb across the brake control line and ground. Turned the key on and nada, nuttin, no trailer found (palm smack). Went to bed and licked my wounds all night.
10. By morning decided my theory was sound and it was the implementation that was flawed (shucks, I'm never wrong :mrgreen: ) and went back to Wally World and bought a trailer stop light (big bulb) Back to the trailer storage lot (no macarena) and clipped the stop light across the pins. Turned the key on and VIOLET (who is obviously some frenchman's sister) there is a message on the dash that said trailer connected. Press the brake pedal and the bulb lights up, etc.
11. Long story short (way late for that, eh) I have connected the stop light bulb across the brake control line and ground (on the trailer side) and plugged the trailer into the truck and everything works as it should, hydraulic pump runs, brake lights light up, brakes clamp up tight..
Why it used to see the Brake rite controller I have no answer. Obviously something changed on the Brake Rite, resistor smoked, etc. (shrug)
1. Took the trailer and truck to a trailer repair place. They went through the Brake Rite system and declared it working properly on their test box.
2. They applied the test box to the truck and declared the truck's brake controller was working.
3. Plug the trailer into the truck and no joy.
4. Plugged the trailer into another GM truck and no joy.
5. Talked to Brake Rite and he gave me the secret test procedure for testing his brake controller and pump. It passes with flying colors.
7. Went back to the trailer repair place and discussed at length. He finally told me I am the third truck he has seen that has problems with the GM ITBC recognizing electric over hydraulic trailer brake systems. It apparently works fine with electric solenoid brakes. He solved the other two customers problem by disabling the GM ITBC and installing an aftermarket controller. That rubs the fur on my check book the wrong way and I declined his "fix".
6. Talked to the local GM dealer and he says he is aware that the GM ITBC has problems with electric over hydraulic trailer brakes. He says GM has not put out any service bulletin on how to deal with this problem and declined to 'work' on the truck.
7. Spent considerable time on the internet researching the problem and it is indeed a problem. Noted in a couple of reports their controller works fine with electric brakes (solenoids) but not with electric over hydraulic. Thought about the difference between the electric brakes (solenoid) and electric over hydraulic and decided the ITBC senses or pings the brake control line (blue) for the presence of the solenoid windings.
8. Measured the input resistance of the Brake Rite controller and got roughly 160 ohms. Found an electric brake trailer out in the storage lot and measured the input resistance of the braking wire and got roughly 0.2 ohms (almost a dead short). Put on my thinking cap and decided if I shorted the brake control wire on the truck bumper (blue) to ground (white) it would trick the ITBC into thinking there was a trailer plugged in. So I did. The ITBC sneered and said "check your trailer wiring buddy", and proceeded to ignore me otherwise. I was a bit put out by the 'sneer' in the glowing message, but I had learned something. The ITBC does indeed check the resistance (impedance) of the brake control line to see if a trailer with brakes is plugged in. An open circuit is no trailer brake and something less than a short is a 'brake' being present. So how much less than a short is needed?
9. Went to Wally World and got a trailer side marker light with a bulb and waltzed back to the marina doing the macarena across the lot because I am sooo smart. Jumped the bulb across the brake control line and ground. Turned the key on and nada, nuttin, no trailer found (palm smack). Went to bed and licked my wounds all night.
10. By morning decided my theory was sound and it was the implementation that was flawed (shucks, I'm never wrong :mrgreen: ) and went back to Wally World and bought a trailer stop light (big bulb) Back to the trailer storage lot (no macarena) and clipped the stop light across the pins. Turned the key on and VIOLET (who is obviously some frenchman's sister) there is a message on the dash that said trailer connected. Press the brake pedal and the bulb lights up, etc.
11. Long story short (way late for that, eh) I have connected the stop light bulb across the brake control line and ground (on the trailer side) and plugged the trailer into the truck and everything works as it should, hydraulic pump runs, brake lights light up, brakes clamp up tight..
Why it used to see the Brake rite controller I have no answer. Obviously something changed on the Brake Rite, resistor smoked, etc. (shrug)