Be alert when the ABS warning light comes on; small issues can lead to big problems.

When evaluating whether a car is good or bad, the most important factor is definitely not its power performance or load capacity, but the safety performance that is closely related to the lives of drivers. The best way to measure a vehicle's safety performance is its braking ability, with the most direct indicator being the braking distance.
 

As the country places increasing emphasis on the safety performance of trucks, related requirements are becoming more stringent. Some electronic brake assist systems have gradually matured and become industry standards, with ABS being the most essential. However, unlike mechanical components, these electronic parts can leave many truck drivers at a loss when they fail, especially since they are critical components related to life safety. So today, let's take a good look at ABS.

● What is ABS?

According to Baidu, the entry defines it as: Anti-lock Brake System (ABS). Its function is to automatically control the braking force of the brakes when a vehicle is braking, preventing the wheels from locking up and keeping them in a state of rolling and sliding (with a slip rate of around 20%) to ensure that the contact between the wheels and the ground is at its maximum.

This might sound a bit complicated, but in fact, it is an electronic control system used to monitor and control the braking force on the wheels during vehicle braking. It does not have braking capability itself and does not directly participate in braking; instead, it works by controlling the conventional braking system.

Although the widespread adoption of ABS systems has not been particularly long, their development can be traced back to the early 20th century. By the late 1970s, the rapid advancement of digital electronic technology and large-scale integrated circuits laid the technical foundation for practical ABS systems. Many companies subsequently developed various types of ABS systems. The introduction of more economical ABS devices, as well as rear-wheel ABS or four-wheel ABS systems suitable for light trucks, created conditions for the rapid popularization of ABS.

● Why install ABS:

Truck drivers who have ridden bicycles know that when braking hard at high speeds, it is easy to perform a stylish skid. This is actually because during braking, locked wheels have very little lateral friction with the road surface, which easily leads to skidding and loss of control.

On a bicycle, this can be considered a cool stunt, but if a truck encounters this situation, it could very likely cause a serious accident. Therefore, ABS (Anti-lock Braking System) is needed. It monitors wheel speed at all times and adjusts braking force when the wheels are about to lock.

This system controls and adjusts brake air pressure to prevent wheel lock-up, enhancing directional stability during braking, ensuring vehicle controllability, and preventing skidding or fishtailing. At the same time, it can shorten braking distances on poor road surfaces, effectively improving the operational safety of heavy vehicles.

According to global research data from relevant organizations, compared with vehicles without ABS, vehicles equipped with ABS can reduce braking distances by up to 10% on normal roads and by 30% on icy or slippery roads.

In addition, the advantages of ABS also include: eliminating the possibility of complete wheel lock, reducing tire wear and maintenance costs; reducing the driver's mental burden; maintaining vehicle steerability during emergency braking, which lowers the likelihood of traffic accidents. Therefore, the ABS system is also considered one of the most important safety technology achievements in automobiles since the adoption of seat belts.

● ABS Control Principle:

As mentioned above, the ABS system itself does not have braking capability; it works by controlling the conventional braking system. The following explains its control principle.

Simply put, ABS installs a speed sensor on each wheel. These wheel speed sensors (monitoring wheel speed) continuously provide ABS with wheel speed information.

When the wheel speed is normal and there is no tendency to lock: the solenoid valve connects the brake control valve with the brake chamber. At this stage, the braking circuit is exactly the same as without ABS, and the air pressure in the brake chamber equals the output pressure of the brake control valve. The output pressure of the brake control valve is proportional to the depth of the brake pedal. At this stage, you will clearly feel a linear relationship between the depth of pressing the brake pedal and the braking force – the deeper you press, the greater the braking force.

When the wheel speed sensor signals a tendency for the wheels to lock: ABS cuts off the airflow between the brake control valve and the brake chamber. At this point, the brake chamber is no longer connected to the braking control side, and the pressure in the brake chamber remains unchanged and is not affected by the pedal.

If the wheel still tends to lock: ABS will connect the brake chamber to the exhaust pipe, allowing the compressed air in the brake chamber to be released through the exhaust pipe, thereby reducing the internal pressure and lowering the braking force to relieve the wheel lock tendency. After the wheels return to normal, the system resumes the first stage.

Of course, the braking process with ABS intervention is not accomplished in one go, but goes through multiple cycles of the three stages mentioned above, gradually reducing the vehicle speed. When the speed drops below a certain value, the ABS will stop working. At this point, you can directly control the vehicle to come to a complete stop using the brake pedal. 

Therefore, when a vehicle equipped with ABS requires emergency braking, the driver should first quickly press down the clutch pedal, and then firmly press the brake pedal to bring the wheels close to locking, which will activate the ABS. 

● ABS Fault Diagnosis 

Earlier, we learned about the working principle of ABS. Now let's talk about how to diagnose ABS faults. As everyone knows, if the ABS warning light turns on while driving, it indicates that there is a problem with the ABS. At this time, normal braking will still work, but timely inspection and repair are necessary.

But as an electronic brake assist system, ABS failures often involve circuit faults in components like wheel speed sensors, which require the use of specialized diagnostic tools that truck drivers usually don’t have. Of course, besides that, there is a simpler and quicker method — flash code diagnosis.

Flash code diagnosis involves reading fault codes based on the number of flashes of the warning light. By referring to the fault code table, you can know what the fault is. Originally, the ABS warning light was used to indicate a fault in the ABS system and to display flash codes, but now the ABS warning light only illuminates to indicate a fault, and the fault code is displayed via the ASR warning light flashes.

The method to read it is straightforward: observe the flash pattern, for example, four quick flashes followed by a pause, then two flashes, repeating in this cycle — this represents fault code 42. Truck drivers can then compare it with their vehicle’s fault code chart.

● Editor’s Note:

In actual use, many truck drivers see the ABS warning light and don’t pay much attention because they feel the brakes still work, that there’s no major issue, and there’s no need to go to a repair shop for such a minor problem, which seems like a waste of time and money. However, in an emergency, if the ABS is malfunctioning, it can easily lead to an accident, and regrets would come too late. So here, we remind all truck drivers to take ABS seriously and have it checked and repaired in time. If there’s anything else you want to know, feel free to leave a comment.