here is a copy of my monthly article i write in a well known truck magazine that might help.
ABS WARNING LIGHTS?
ABS and EBS warning lights!
How do you know what your warning light on your trailer or in the cab should be doing,
For starters there are only three main warning light sequences that are out there.
They are:
ON/OFF at standstill
ON and remain on until the vehicle is driven above 7kph
ON/OFF/O and remain on until the vehicle is driven above 7kph
The three main light sequences are used by knorr bremse, wabco and haldex,
with the invention of programmable warning lights in EBS systems it has become a bit harder to know what yours should be doing but with a couple of simple tests you can find out, these tests are as follows:
For trailers:
If you have an iso 7638 connector (ABS socket) on both your truck and trailer start by just connecting this and turn on the ignition, the trailer warning in the cab should come on, if the light goes ON/OFF then that is the sequence, if the light stays on then drive the truck and trailer above 7kph, if it goes out then that is your sequence, if the light stays on there is a fault in the system and you will have to fix it before you can go any further.
For trucks:
Turn on the ignition and look at the light, if it goes ON/OFF then that is the sequence, if the light stays on then drive the truck above 7kph and if the light goes out then that is the sequence, if the light stays on after you have driven off there is a fault in the system and you will have to fix it before you can go any further,
How the warning light works:
The warning light is controlled by the electronic control unit (ECU) when you turn on the ignition the ecu checks the external components to see if they are ok, after this initial test some systems will turn the warning light out and it will only come on if a fault appears when then vehicle is driven, if the warning light stays on then there is either a fault in the system or the ecu is waiting to see the wheel speed signals from the sensors, once the ecu sees signals from all the sensors it will turn the warning light out,
All ABS/EBS warning lights on all the systems have one thing in common, this is that when the vehicle is driven above 7kph the light should go out, if your light is on when you are driving you have a fault in the system.
(note: some electronic dashboards don’t show a warning light until a fault appears)