ABS System Fault
The automobile anti lock braking system, namely ABS, automatically adjusts the pressure in the brake pipe according to the wheel speed when the automobile is braked, so that the wheel is always in the sliding state of locking and rolling, especially in emergency braking. It will brake intermittently, that is, brake - release - brake, so as to avoid danger. [1] The anti lock braking device carries out pulse braking of braking release braking at the frequency of 6 ~ 10 times per second. The electronic intelligent control mode is used instead of manual mode to prevent wheel locking, so that the wheels can always obtain the maximum braking force and maintain flexible steering. When the wheel wants to lock up, reduce the braking force, and when the wheel will not lock up, increase the braking force. Such repeated actions make the braking effect the best.
Using the device can reduce the braking distance and ensure that the steering control is still effective during braking. In particular, emergency braking can make full use of the peak adhesion performance of tires, improve the anti sideslip ability of vehicles, shorten the braking distance and give full play to the braking efficiency.
In use, if the ABS system fails, the warning lamp will light up and must be stopped for treatment or repair in time. Common troubleshooting methods of ABS system are as follows:
1. Pressure relief of ABS system
The general pressure relief method of ABS system is: turn off the ignition switch (off), and then step on the brake pedal repeatedly for more than 20 times. When the pedal force increases significantly, that is, the hydraulic power of stepping on the pedal is not felt, the ABS system is relieved. Pressure relief is usually required when repairing the following components: any device in the hydraulic control unit, accumulator, electric pump, solenoid valve body, brake fluid tank, pressure warning and control switch, rear wheel distribution proportional valve, rear wheel brake cylinder, front wheel brake cylinder and high-pressure brake fluid pipeline, etc.
2. ABS system computer replacement
Replace the original vehicle computer with a normal computer, observe the working condition of ABS system, and identify whether the original vehicle computer is faulty through comparison. When replacing, turn off the ignition switch, remove the harness plug on the computer, replace the normal computer, plug in all harness plugs, and turn on the ignition switch. Then start the engine, and the red brake lamp and ABS lamp shall display the normal state of the system.
3. Wheel speed sensor adjustment
The dirty sensor plug and the air gap of the sensor do not meet the requirements, which will lead to poor operation of the sensor. It shall be adjusted to restore the normal working state. The adjustment of the sensor can be completed by sticking the paper gasket close to the end face of the sensor head. When the car is running, the paper gasket will disappear naturally with the rotation of the sensor ring gear.
Adjust the front wheel speed sensor (take Tanfu ABS as an example): lift the vehicle, remove the corresponding front wheel tire and wheel device, loosen (fasten the sensor head) bolts, remove the sensor head through the disc brake fender hole, remove the metal or dirt on its surface, scrape the end face of the sensor head, and paste a new paper gasket on the end face of the sensor head (mark "F" to indicate the wheel), The thickness of the paper gasket is 1.3mm. Loosen the bolt of the fixed bushing of the sensor support, rotate the bushing, provide a new locking dent surface for the fixed bolt, install the sensor head into the bushing on the support through the disc brake fender hole, and confirm that the paper gasket is attached to the end face of the sensor head and does not fall off during the whole installation. After installation, the wiring on the sensor is in good contact. Push the sensor head to the top of the sensor ring gear until the paper gasket contacts the ring gear. Tighten the fastening bolt with a torque of 2.4 ~ 4N · m to position the sensor head. Reinstall the tires and wheels, put down the car, start the engine for road test. If the ABS fault indicator does not light up, the system is normal and the sensor is good. Otherwise, the ABS system still has faults and needs further maintenance.
Adjust the rear wheel sensor: the same as the front wheel sensor. Lift the car, remove the rear wheel, brake caliper, transmission device and sensor head, clean its surface, paste a paper gasket (Mark R) on the end face of the sensor head, and the thickness of the paper gasket of 35 pin computer ABS is 0.65mm. Reinstall the sensor head, tighten the fixing bolt, push the sensor head to move towards the top of the sensor ring gear until the paper gasket contacts the ring gear, maintain this state, and tighten the fixing bolt with 2.4 ~ 4N · m torque to position the sensor head. Reinstall the Tong and wheel, put down the car, and finally conduct a road test.
If the wheel speed sensor is found to work poorly, use a digital multimeter to measure the resistance of its coil. High resistance is open circuit and low resistance is short circuit, so the sensor head needs to be replaced.
4. Maintenance of hydraulic control device
Before overhauling the hydraulic control device, the pressure shall be relieved according to the general method. When removing the hydraulic control device, unplug the solenoid valve, remove the O-ring, lubricate the solenoid valve O-ring with clean brake fluid, install the solenoid valve with good performance, tighten the fixing bolts alternately with 4 ~ 5N · m torque, fix the solenoid valve and plug in the wiring plug.
5. ABS system replacement
Poor contact of ABS harness connector, corrosion, fracture of harness and damage of external shield will lead to abnormal operation of anti lock braking system, which must be replaced. The harness plug is usually replaced together with the harness. When individual harness plugs are damaged, they can be replaced. The ground wire and shield wire shall be welded firmly. The harness plug is plastic and can only be replaced together with the harness. The harness plug must be firmly inserted to prevent poor contact. After the connector is inserted, insert the clip.
6. Bleeding of ABS system
If there is air in the ABS system, it will seriously interfere with the adjustment of braking pressure, resulting in the loss of ABS system function and abnormal operation. In particular, after the ABS is repaired, bleed according to the provisions of the "maintenance manual".
7. Hydraulic element leakage inspection
When checking the leakage of hydraulic components, turn on the ignition switch until the hydraulic pump stops running, and then wait for another 3min to make the whole hydraulic system stable. Check the pressure gauge. If the system pressure drops within 5min, it indicates that there is leakage in the hydraulic system. Then check whether the hydraulic element itself leaks or its external system leaks, repair them respectively, and replace the worn parts or assemblies if necessary.
Post time: Oct-15-2021