ABS Wheel Speed Sensor
Most of modern cars equip with ABS wheel speed sensors. The parts are so important that they save lives sometimes. They detect wheel speeds and avoid rollover during car accidents.
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When the vehicle's anti-lock braking system has problems, the fault indicator keeps on. The system fails. The wheels go skidding on the road in the process of braking. When you put the brake pedal to the metal, the wheels lock and lose steering ability.
During the repair of the anti-lock braking system, first, we should check whether there are problems in the ABS or the basic braking system. If it's the latter, we should check its appearance for brake fluid leakage, loose plugs, low brake fluid level, damage to the brake master cylinder, brake wheel cylinder and vacuum booster. If the routine inspection result is pleasing and the fault indicator keeps on, problems may appear in the ABS ECU, wheel speed sensor, brake pressure regulator and other components.
If the ECU doesn't work, the main reason is that the brake pressure regulator, which regulates the braking force of the wheels, doesn't receive control commands or receives the wrong control commands. The regulator can't work properly. The wheel-braking force can't finish self-regulating.
The wheel speed sensor detects the movement of the wheels. The sensor converts the wheel speed into an electrical signal to the ABS ECU. When the ABS wheel speed sensor fails, the signal sent to the ECU is inaccurate, which causes incorrect judgment by the ECU. The braking pressure regulator to adjust the braking pressure doesn't meet the vehicle's braking needs. The anti-lock braking system control will be inaccurate.
The brake pressure regulator automatically adjusts the pressure of the brake distributor pump in terms of the ECU control instructions. Failure changes the flow direction and quantity of the brake fluid in the brake line. The braking force of the entire brake system is impossible to self-regulate in terms of the wheel braking conditions, which causes the failure of the anti-lock braking system.
Step 1: Connect diagnostic equipment and check the ECU control circuit
(1) Check whether the power supply and the hitch wire which enable the anti-lock braking system ECU to work correctly are normal. Check the corresponding insurance device.
(2) If the ECU doesn't work after entering the system by the diagnostic equipment, check the brake signal line. Turn on the ignition switch and use a test light to test the brake signal line. If the light keeps on while pressing the brake pedal, the brake signal voltage measured by the multimeter is about 1V lower than the battery voltage.
If the test light isn't on or the signal voltage can't be measured, the brake switch is damaged, or the line connecting the brake switch has poor contact, or the line is faulty. Now replace the brake switch and overhaul the line. If the above check items are normal, the ECU has problems. Replace the ABS ECU.
Step 2: Read the DTC and make a failure diagnosis of the anti-lock braking system
Test the wheel speed sensor, fuse, indicator circuit, power circuit, ground circuit. All other items are not testable. Except for poor contact and short-circuit problems, all failed components are unrepairable and should be replaced directly with new parts.
(1) Read the DTC. Check and repair the failed parts in terms of the information served by the diagnostic equipment.
(2) Test the wheel speed sensor in terms of the DTC.
Measure the resistance of the magnetic induction wheel speed sensor. The resistance of the front wheel speed sensor measured by the multimeter is about 1300Ω. The resistance of the rear wheel is about 1500Ω. If the actual number is much higher or much lower than these two, then the sensor is failed and needs a replacement.
Measure the AC voltage of the wheel speed sensor. Turn the multimeter to the AC rms voltage of 2V. Rotate the wheel and measure the induced voltage of the sensor. Under normal circumstances, AC voltage rises with speed. The voltage should be above 0.1V. If the measured value is zero, the sensor has a problem and needs a replacement.
If the wheel speed sensor resistance and AC voltage can't be measured, check if the sensor's connection line is in contact or not and if the connection plug is loose.
(3) Don't destroy the sensor head while dismantling. Don't use the sensor ring as the prying surface. This process damages the ring. Instead, anoint anti-rust oil before installation. Ensure that no impact and brute strength during the installation. Sensor air gaps are adjustable. The non-magnetic plug ruler goes into service during the adjustment. The gap between the sensor head and the gear ring is generally 0.4mm-1.0mm. Check whether the rotor gear ring has cracks, missing teeth and broken teeth. Also, check whether iron filings exist between gear ring teeth.
Test the braking pressure regulator in terms of the DTC
When the DTC shows failures in the electric return pump or solenoid valve, it's impossible to judge whether it's good or not by the appearance or the multimeter. The sound makes it work. When repairing the ABS hydraulic control unit, remember to relieve the pressure first, then do the repair job by rules, avoiding injury from high-pressure oil spraying out.
ABS wheel speed sensors have become essential parts in modern vehicles. We are talking about the key component in the braking system here. You can’t be too careful when it comes to safe driving. Delcoribo makes good products with strong braking force. The remarkable durability helps to resist water, mud, dirt and abrasion.
Everyone can have faith in Delcoribo when talking about this sensor. Engines need stable wheel speed signals to keep the ideal drivability. We take pride in providing our products due to the high-standard manufacture. Apart from the premium quality, people in cars can enjoy better ride comfort, thanks to the constant moving wheels with no mistakes.
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