At our Texa technical assistance centre based near Burnley in Lancashire, we are currently receiving on average 70 calls a day on all manner of Van, Car, Truck, Bus, Coach, Agricultural, Trailer and Marine repairs and faults. We are continuing to receive more and more calls from our diagnostic tool users with trailer related faults, these may be ABS (Antilock Braking System) or EBS (Electronic Braking System) related faults or even foundation braking problems.With trailers, virtually every component is underneath the chassis and is totally exposed to the elements, this can lead to water getting into components creating corrosion, high resistance values or even short circuits. These faults will bring on the trailer ABS warning light and take the trailer off the road.
By using our diagnostic equipment, this will help speed up your repairs, by being able to communicate with the ECUs, read and erase error codes and being able to view live data, activating components and having the ability to make settings and adjustments on a vast majority of trailer braking systems from the early ABS to the latest generation 2 EBS. One of the most common problems is down to wheel sensors; there can a multitude of faults that could generate an error code relevant to wheel sensors. These could be an electrical fault from the sensor itself caused by water ingress or damage, a short or open circuit of the sensors internal winding.
A simple multimeter test across the sensor terminals can soon eliminate a sensor there, should there be a resistance value of approximately 1200 ohms depending on the type of sensor used. You also need to check for an insulation breakdown in the sensor, there should be no continuity to earth from the sensors terminals.
There could also be a mechanical fault causing problems, these can be down to corroded teeth on the poll wheel. Many disc brakes have the poll wheels cast into the actual disc, carefully inspect the teeth for corrosion or damage, replace the discs as necessary. Excessive play in wheel bearings, unevenly worn or incorrect tyre sizes or the air gap between the sensor and the poll wheel can also cause these problems.
One thing to take careful note of is what speed the ABS light comes on at; if it is a mechanical fault the ABS light will normally illuminate at exactly the same speed every time. Another common problem is down to the ISO7638 cable, be it the one between the truck and the trailer or the lead going from the head board down to the ECU. If there is a power supply issue or earth to the ECU it won’t work or communicate with your diagnostic equipment.
Many expensive trailers ECU’s have been replaced unnecessarily when the fault is down to a pin pushed back in the head board socket.
Trailer ECUs should also have a backup power supply from the brake light circuit, if the ECU is not powered try pressing the foot brake to give is a back up power supply, if the system then powers up the ECU has been eliminated. These simple checks will help speed up your repairs and help to prevent expensive incorrect diagnosis.
For more information: www.texa.co.uk