ABS, EBS and electronic safety systems on heavy vehicles

The brake system on a heavy vehicle is already safety-critical in itself but modern trucks also have a series of electronic systems built on top of the compressed air brakes which must prevent wheel lockup distribute braking force optimally and in some cases intervene before the driver does. As a truck mechanic you must know both the purpose of and troubleshooting on these systems.

The anti-lock braking system (ABS) monitors each wheel's rotation speed via sensors and automatically releases brake pressure to that wheel if it is about to lock. A locked wheel loses steering control and can extend braking distance on slippery surfaces, so ABS is today mandatory on new trucks, buses, and trailers in the EU.

The electronic braking system (EBS) builds on air brakes by letting a control unit electronically calculate and distribute the braking force between the axles instead of purely mechanically-pneumatic. This provides faster reaction time, better interaction between tractor and trailer, and makes it possible to integrate additional safety functions in the same system. EBS typically works together with ABS, so the anti-lock function is built into the same electronic brake layout.

Because ABS and EBS are tightly coupled to the CAN bus and receive signals from wheel sensors pressure sensors and other control units troubleshooting always starts by reading fault codes from the brake control unit. A single faulty wheel sensor can trigger a fault that limits the entire vehicle's braking assistance and correct calibration after repair is critical — some systems require a calibration routine to be performed with diagnostic equipment after a component is replaced.

• 01Check wheel sensors and their cabling for damage and correct air gap.
• 02Read error codes from the brake control unit before and after repair.
• 03Perform the manufacturer's calibration routine after replacement of brake components where required.
• 04Test warning lights and alarm functions at startup, as part of each inspection.

Electronic safety systems make heavy vehicles significantly safer but also require that you as a mechanic understand the interplay between mechanics, pneumatics and electronics — a corrected component that is not properly calibrated can still leave a safety system out of function.