Pay attention when the ABS warning light is on; a small problem can cause big issues.

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

As the country increasingly emphasizes the safety performance of trucks, related requirements are becoming stricter. Some electronic assisted braking systems have gradually matured and become industry standards, among which ABS is unavoidable. However, unlike mechanical components, once these electronic components fail, many truck drivers are at a loss, especially when it comes to critical parts related to life safety. So today, let's take a closer look at ABS.

● What is ABS?

The explanation given by Baidu is: Anti-lock Braking System (ABS) is an anti-lock braking system. Its function is to automatically control the braking force of the brakes when the vehicle is braking, so that the wheels do not lock, staying in a state of rolling and slipping (with a slip rate of about 20%) to ensure that the adhesion between the wheels and the ground is at its maximum.

This explanation may be a bit complex. In fact, it is an electronic control system used to monitor and control the braking force of the wheels during vehicle braking. It does not have braking ability itself and does not participate directly in braking but works by controlling the conventional braking system.

Although the full adoption of ABS systems has not been very long, its development can be traced back to the early 20th century. By the late 1970s, the rapid development of digital electronic technology and large-scale integrated circuits laid the technical foundation for the practical implementation of ABS systems. Many companies developed various forms of ABS systems one after another. The emergence of economical ABS devices, as well as rear-wheel ABS or four-wheel ABS systems for light trucks, created conditions for the rapid popularization of ABS.

● Why install ABS:

Truck drivers who have ridden bicycles should know that when braking hard at high speeds, it is easy to perform a flashy drifting maneuver. This is actually because during braking, the locked wheels have very little lateral friction with the road surface, making it easy to skid and lose directional control.

On a bicycle, it can be a stylish stunt, but if a truck experiences this, it can easily lead to a serious accident. Therefore, an anti-lock braking system (ABS) is needed at this time. It can monitor wheel speed at all times and adjust brake force when the wheels are about to lock.

This system prevents wheel lock by controlling and regulating brake air pressure, enhancing directional stability during braking, thereby ensuring vehicle controllability, avoiding skidding or fishtailing, and also shortening stopping distances on poor road surfaces, effectively improving the operational safety of heavy trucks.

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

In addition, the advantages of ABS also include: eliminating the possibility of wheels completely locking up, reducing tire wear and maintenance costs; alleviating the mental burden on the driver; maintaining vehicle controllability during emergency braking, reducing the likelihood of traffic accidents. Therefore, the ABS system is also considered one of the most important technological achievements in automotive safety since the adoption of seat belts.

● ABS Control Principle:

As mentioned above, the ABS system itself does not have braking capability, but works by controlling the conventional braking system. The control principle is as follows.

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

When the wheel speed is normal and there is no tendency for locking: the solenoid valve connects the braking control valve and the brake chamber. At this time, the brake circuit is exactly the same as when there is no 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 signal from the wheel speed sensor determines that the wheel has a tendency to lock: ABS will cut off the air path between the brake control valve and the brake chamber. At this time, the brake chamber is no longer connected to the control side, and the pressure inside the brake chamber remains unchanged, unaffected by the pedal.

If the wheel still has a tendency to lock: ABS will also connect the brake chamber to the exhaust pipe, allowing the compressed air in the brake chamber to be discharged through the exhaust pipe, thereby reducing the chamber pressure, which decreases braking force and releases the wheel lock tendency. Once normal, it returns to the first stage.

Of course, the braking process with ABS intervention is not accomplished in a single step; it involves multiple cycles of the above three stages, gradually reducing the vehicle speed. When the speed drops below a certain value, the ABS will no longer operate. At this point, the vehicle can be brought to a complete stop directly by controlling the pedal.

Therefore, when a vehicle equipped with ABS requires emergency braking, the driver should first quickly press down the clutch pedal, and then strongly press the brake pedal to make the wheels tend to lock, thus activating the ABS.

● ABS Fault Diagnosis

Above we have understood the working principle of ABS. Next, let's talk about how to diagnose ABS faults. As everyone knows, if the ABS light turns on while driving, it indicates that there is a fault in the ABS. At this time, although conventional braking still works, timely maintenance is also required.

But as an electronically assisted braking system, ABS failures often involve circuit faults in components such as sensors, which require a professional diagnostic tool—something truck enthusiasts usually don’t have. Of course, apart from that, there is also a relatively simple and quick method: flash code diagnosis.

Flash code diagnosis means reading the fault code based on the number of flashes of the warning light. By referring to the fault code table, you can determine what the problem is. Originally, the ABS warning light was used to indicate an ABS system fault and for flash code diagnosis, but nowadays, the ABS warning light only lights up to indicate a system fault, and the fault code is displayed through the ASR warning light by flash code.

The method of reading is very simple: observe the flashing pattern of the light. For example, a quick flash four times, pause, then flash twice again, and so on in a cycle—this represents fault code 42. Truck enthusiasts can then compare it with the fault codes specific to their vehicle model.

● Editor’s Note:

In practical use, many truck enthusiasts notice the ABS warning light but don’t pay much attention because they feel the brakes still function and there’s generally no problem, so there’s no need to take the trouble to go to the repair shop, which would waste time and money. But in an emergency, if the ABS is malfunctioning, it can easily lead to an accident, and by then it will be too late to regret. Therefore, we remind all truck enthusiasts to take ABS seriously and have it inspected promptly. If there are any other questions you want to know about, feel free to leave a comment in the section below.