Electronic Brake System (EBS) Trailer Testing With ISOCheck
October 11th, 2017
What Is The ISO EBS Truck & Trailer Lead
How does the EBS truck & trailer Susie lead work?
Everyone seems to have there own ideas how it works, ranging from; “if it’s not plugged in your trailer brakes wont work”, & “it’s only a back up power anyway”
Both are incorrect!
The truth is…
The Electronic Braking System (EBS) Susie or the ISO 7638 (its correct name) is essential for the trailers Electronic Braking System (EBS) to operate correctly.
So, if a truck has an ISO7638 socket a tractor and trailer must be connected with an ISO7638 Susie and the EBS must be working correctly!
Also this means the EBS warning light the truck operator should be checking is in the cab and not the one on the trailer headboard (if there is one).
This is where the problems start, how does the EBS lead actually work, well this is how:
Pin 1 in most trucks is permanent live
Pin 2 is switched ignition live
Pin 3 is common return to battery negative
Pin 4 is common return to battery negative
Pin 5 is the warning light control (positive)
Pin 6 is “CAN” High
pIn 7 is “CAN” Low
Pin 5 which is the warning light control wire, this pin seems to be continually misunderstood. Some people think pin 5 is controlled by the trucks EBS system or even by the truck itself, both of these are incorrect, how it works is quite simple, a basic explanation is detailed below:
Power from the truck battery routes to a fuse, then to the ignition switch and then to the warning light in the dash board, finally then to pin 5 in the socket.
When an EBS Susie ISO7638 lead is connected to the trailer the trailer EBS system sees 24 volts down pin 5, which and then reduces that voltage inside the trailer ECU to below 5 volts (earth) which then activates the EBS light on in the truck cab.
Once a truck & trailer is in motion and the the trailer EBS system is happy with the wheel speed signals, the ecu then raises the voltage back up to 24 volts and the warning light in the cab goes out, if a fault appears when a truck & trailer is on the road, the ecu lowers the voltage again activating the In Cab Warning Light.(Please Note This Is a Basic Description).
An easy way to test the truck & trailer ISO Connection socket is the ISOCheck
What Is The ISO EBS Truck & Trailer Lead?