ABS on trailers

The FMSCA or DOT regulations make no mention about the ABS having to work on the trailer as I know of. The regs do state that any trailer manufactured after a certain date had to be equiped with ABS. I would document it on your logs just to CYA. Say you end up in an accident. Well the if you noted that the ABS didn't work on that trailer when you picked it up it may help you if you end up in court. That won't be perfect solution to get you out of the situation, but at least it shows that you were diligent with your pretrips and that the carrier ignored the repairs.

 

Technically the law states the brakes must be fully functional with no part of the system disconnected or not working. They really don't do a good job making this clear with regard to ABS, but it is a part of the system. If the ABS isn't working on a trailer here in Canada they can't get a safety sticker! If a truck you worked on, or certified is involved in an accident and the ABS isn't working and there is a law suit because the mechanic didn't write up or repair the ABS we all know what happens. Always cover your ###!

 

Does the ABS not work at all, the light stay on all of the time, or just come on when you apply the brakes?

 

I depends on the system and the year. Newer trailers use the green trailer trailer cord from the truck that have the center pin powered with ignition power all the time when the key is turned on. This powers the ABS ECU. On trailers built up to around 98-2000 the ABS ECU will get its power from the brake light circuit only. The ECU only takes a split second to boot up and start working. Trailers built 2001 and after are required by law to ABS powered constanly from the Blue wire auxiliary pin on your cord. Most systems will turn the light on and off and do a system check at key-on, or when the trailer is plugged in. If you are at the back of the trailer you will hear the modulators clicking during the check. Some types the ABS lights come on when you hit the brakes and go out. This is normal. Basically, if the light never comes on there is problem, if the light never goes out there is problem. Light on at key-on or plug in then goes out, is normal. Light comes on when braking then goes out is also normal. If you see the light blinking all the time, chances are it is blinking diagnostic codes which indicate a problem aswell.

 

Once you are below5-7 mph, they will not work. I have seen trailers slide to the curb when road very slippery. It is still possible to have just a mechanical problem and not an electronic one. You would almost need someone to watch the rear trailer tires on slippery road while you make a brake application hard enough to lock the wheel up and see if the ABS is working. Or keep an eye for flat spots on your tires as that would be a dead give-away the ABS isn't working either.