What Should You Do When The Trailer ABS Light Comes On?


The safety of semi-trailers in the driving process is very important. The application of ABS in the braking of vehicles is of great significance to improving the security and stability of cars in the process of driving. And the trailer ABS light can play a crucial role. The ABS light on trailer is flashing. This indicates a fault in the system, and its stable working condition is affected. Today I will share some common failure cases and maintenance precautions for the ABS braking system. I hope this helps you when the trailer ABS light comes on.

What is a semi-trailer ABS?

Aluminum Oil Tanker Trailer for Sale
Aluminum Oil Tanker Trailer for Sale

Let’s start by understanding what a semi-trailer ABS is. The semi-trailer ABS refers explicitly to the anti-lock braking system, which is an additional device on the original car braking system to control the stability of the car body during the braking process. The ABS is mainly composed of three parts: wheel sensors, controllers, and regulators. After braking, the ABS mostly achieves the vehicle’s stable control goal by controlling the wheels’ slip rate and wheel speed. The semi-trailer brake is generally an air brake, and the air source comes from the tractor. There are three main parts: emergency relay valve, trailer ABS and brake air chamber. Most failures come from these three large pieces in the absence of air leakage due to improper sealing. Of course, the problem is all-around. All parts related to the air brake will have varying degrees of impact, so the installation should not be taken lightly.

ABS inspection

1. Check whether the connection status of various devices and firmware in the ABS is tight, especially the installation of connectors and cables, and analyze the interference coupling effect of related components and other components. The devices that cause interference should be improved and improved. The upgrade promotes the normal operation of the ABS. In addition, it is necessary to place the trailer ABS light in the “on” position, turn on the car’s power, and check whether the trailer ABS light is displayed normally.
2. Keep the semi-trailer in the running state, and the vehicle speed is 10 kilometers per hour; at this time, the ABS light on semi trailer is in the off state, and it can be determined that the semi-trailer’s ABS is operating normally. If the trailer ABS light is flashing, the ABS is not functioning normally, and its stable working conditions are affected. At this time, the driver should continue to observe the flashing frequency of the trailer ABS light. Different frequencies correspond to fault codes, which must be based on the actual situation. Determine the type of failure, and take targeted improvement measures. For example, if the trailer ABS light flashes alternately with an interval of 1 second, the fault code is 1.1. The specific meaning is that the exhaust solenoid of the left front regulator has a fault. The troubleshooting method is maintenance or replacement.

Why is ABS light on a semi trailer?

If the trailer ABS light is on, this indicates a fault in the system, and its stable working condition is affected. You may need to check all of your wheel sensors. You may have a loose or dirty connection. It is worth mentioning that driving with your trailer ABS light is a bad idea. This is because it indicates that your ABS is not functioning correctly. Your vehicle may not be able to handle heavy braking as it was designed. This is an emergency situation; you should immediately stop driving if your trailer ABS light comes on.

Common faults and solutions

1. The air pressure has been lower than 0.7MPa for a long time, or the trailer has obvious drag brakes during the driving process. ‍‍‍‍The processing method is as follows:
a. Replace the front of the car and troubleshoot the tractor.
b. Check the source of air leakage by applying soapy water, and eliminate “air leakage at the handshake connection,” “pipe joint leakage,” “brake chamber air leakage,” etc.
If it exists, you must check whether the valve body enters water or can see apparent rust. This phenomenon indicates that the trailer air pipeline is not well filtered and dried, and the valve body may need to be replaced.

2. The trailer cannot be started after being parked and has been locked. The processing method is as follows:
a. First, unplug the ABS spiral wire to see if it can normally start to eliminate circuit problems.
b. Put the tractor in the inflating state, unplug the air pipe of the manual valve, and check whether the air pressure of the air outlet is normal (the air pressure should be huge in the inflated state).
c. Check whether the parking brake is in the released state.
d. If there is no problem with the gas circuit inspection, check the axle content for mechanical failure.
In all braking states of the trailer braking system, the safety design ultimately keeps the air supply pipeline unblocked. Both the foot brake of the tractor and the parking brake measures are effective by supplying air to the control pipeline.

Tips for daily maintenance of trailer braking system

No one wants to see their trailer ABS light on all the time. After all, when your trailer ABS light comes on, it means there is a fault that you need to deal with. Here are some daily maintenance tips for the ABS on semi trailer.
1. After receiving the new car, check whether the ABS is working correctly. The working status of the ABS is still checked before the car is reviewed every year.
2. Regularly replace and clean the dryer and filter of the tractor to prevent the dirt in the pipeline from damaging the ABS.
3. Every 15 days in winter (monthly in summer), clean the accumulated water in the leading vehicle and trailer air tank, especially in winter.
4. Every time the axle is maintained, or the brake shoe is replaced, the dust or oil on the surface of the sensor and gear ring should be removed in time.
5. When replacing or maintaining the sensor, pay attention to whether the clamping force between the sensor and the elastic bushing is appropriate (the clamping force should be 120~200N). If it is too small, the elastic bushing must be replaced.
6. Check the ABS wiring harness and air circuit every week for wear, interference, peeling and aging, electric leakage, and air leakage.
7. Check and clean up the dust, rust, and other dirt inside each plug connector every month.
8. Check whether the ABS regulators and ECU fixing bolts and nuts are loose every month and tighten them in time.


In layman’s terms, ABS acts like a driver’s “spot braking” quickly and frequently, but the driver’s “spot braking” frequency cannot be compared with ABS in any way. ABS only works when emergency braking causes the wheels to lock up. When a vehicle equipped with ABS encounters an emergency braking in a dangerous situation, the clutch should be stepped down quickly, and then the foot should be slammed to brake. At the same time, the steering wheel can still be turned to make the vehicle avoid obstacles. If the trailer ABS light is on while the car is running, the ABS is malfunctioning. If you don’t deal with it in time, many safety and quality accidents will be caused. Therefore the role of ABS on semi trailer should be taken seriously and maintained promptly.