Failure phenomenon
A 2014 Aveo Aveo, traveling 56 456km, was sent for repair due to the abnormal sound of the front wheel bearing. After replacing the right front wheel bearing, the owner found that the ABS light was always on and stepped on the brake pedal while driving, it will obviously feel the pedal vibration and elastic feet, accompanied by the sound of "giggling", so it will be sent for repair again.
Fault diagnosis and remove
After picking up the car, first test the car and verify the fault phenomenon. As the owner said, the ABS indicator light is always on, and the ABS starts by mistake during the braking process. Connect the dedicated detector and find that the system has a historical fault code "DTC C1226 00: circuit performance failure of the right front wheel speed sensor". Remove the right front wheel speed sensor and detect it. No abnormality is found. Clear the fault code and conduct a road test. The fault disappears and the vehicle is delivered.
A few days later, the car came into the station again for repair, and the failure phenomenon was exactly the same as before, and the owner complained.
After receiving the car, connect the dedicated diagnosis equipment and retrieve the fault code. As before, there is still a historical fault code "DTC C1226 00: circuit performance failure of the right front wheel speed sensor" in the system ". Query maintenance manual to learn more about the exact meaning of the fault code: no data is transmitted to EBCM for the right front wheel sense of speed transmission. When the faulty car brakes, the pedal shakes and ABS starts by mistake, indicating that EBCM monitors that the rotating speed of the right front wheel is obviously lower than that of other wheels (or the rotating speed is "0"), so ABS starts to work.
Considering that the failure phenomenon of the car occurs after the right front wheel bearing is replaced, the cause of the failure should have a great relationship with the bearing. The car uses hall-type digital wheel speed sensor (Figure 1), and the signal generator (magnetic coding ring) of the sensor is integrated on the oil seal of the front wheel bearing (Figure 2). If the magnetic coding ring integrated with the oil seal is damaged, it may lead to the above failure phenomenon.
Figure 1 Hall wheel speed sensor
Figure 2 magnetic coding ring integrated on bearing oil seal
Remove the right front axle to expose the magnetic coding ring on the bearing, and carefully check that there is a very slight depression on the magnetic coding ring, about 1mm. If you do not check carefully, it is easy to ignore. This slight "depression" causes the gap between the coding ring and the sensor to become larger, and the sensor cannot stably sense the rotation of the wheel (figure 3).
Fig. 3 clearance comparison of magnetic coding ring on bearing
The signal generator of this split Hall wheel speed sensor, namely the magnetic coding ring (Fig. 4), is usually integrated on the front wheel bearing. If the code ring is damaged during bearing installation or installation, it will cause failure.
Fig. 4 sensor structure
Therefore, before installation, be sure to check whether the coding ring on the new accessories is in good condition. Pay attention to the installation direction of the bearing and protect the coding ring at the same time. After installation, make sure that the coding ring is in good condition, the gap with the sensor is normal (figure 5).
Fig. 5 inspection method of bearing magnetic coding ring
After replacing the new right front wheel bearing with intact magnetic coding ring, the fault of the car was completely eliminated.
Maintenance summary
The reason for the failure of the car is that the magnetic code on the newly replaced right front wheel bearing has concave deformation, which seems to be caused by the quality of the accessories. However, after further investigation, what is the reason for the defects of the accessories? Is it caused by the quality of accessories, improper transportation and storage, or mistakes in the installation process? It is difficult to distinguish clearly. However, if you know the principle and structure of the sensor very well, check carefully before installation, pay attention to key points during installation, and confirm after installation, the failure phenomenon will not appear in front of the car owner.
Expert review
Luo News
The fault of this car is relatively simple. Because the car appears after the right front wheel bearing is replaced, the fault point can be found quickly by reading the ABS system fault code and data flow of the car. When the car is running, it can be found through the data flow that the right front wheel shows that the wheel speed is inconsistent with the other three wheels. The main reason is that the gap between the right front wheel speed transmitter and the magnetic coding ring is too large, which leads to the signal instability, and because the signal of the right front wheel is inconsistent with the other three wheel signals, the ABS fault indicator light of the dashboard is lit. For the ABS system, once the ABS fault indicator lights up, the ABS system will stop working and the braking system will enter the traditional regular braking.
