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There Is A Problem With The Wheel Speed Sensor Of Abs System. How To Solve It

We have encountered a lot of ABS faults, but we share less. Today, the car craftsman and your masters repair a car with ABS fault light on. By the way, let’s talk about the wheel speed sensor. When the car came, the driver said that the ABS light on the instrument was always on, and the car failed the annual examination. Enter the system with the diagnostic instrument (machinist C80) and report the “left front wheel speed sensor” fault code.

Verification failure of wheel speed sensor 

In order to verify the accuracy of the fault code, lift the two rear wheels with a jack and rotate them by hand. At the same time, observe the data flow. The voltage of the left rear wheel and the right rear wheel on the diagnostic instrument is 0.3 ~ 0.4V, and the corresponding wheel is accurate, indicating that the sensors of the left and right rear wheels are normal. Lift and rotate the left front wheel again, the left front wheel speed data is always displayed as 0, there is no change, and the left front wheel speed signal is indeed abnormal.

Troubleshooting of wheel speed sensor

These are the reasons for the abnormal wheel speed:

1. The sensor is damaged or the gap is too large;

2. ECU to sensor circuit fault;

3. ECU is damaged.

  • From simple to difficult, check one by one, unplug the left front wheel speed sensor plug, and use a multimeter to measure the 5V voltage between the two wires from ECU, indicating that the sensor circuit and computer output voltage are normal. Re measure that the resistance of the wire harness at the sensor end is infinite, and the secondary pipe stop is also infinite, indicating that the sensor has been damaged. Install a new sensor, disassemble the left front wheel, install a new sensor, and adjust the gap (the standard is 0.5 ~ 1.5mm). During installation, first level the sensor head with the end face of the mounting seat, reinstall the wheel core (with sensor signal ring gear), rotate the wheel, observe the data flow, the signal voltage of the left front wheel is 0, and slowly knock the sensor into the wheel core, Until the voltage just shows 0.4 ~ 0.5V during rotation (remember not to knock in too fast or too much, and be careful that the sensor head and the signal gear ring touch and damage the sensor). Turn off the ignition switch and turn it on again. The ABS lamp on the instrument has automatically extinguished after self inspection. During the road test, all signals are normal and ABS returns to normal.
  • The ABS wheel speed signal of some models is abnormal. After repair, no fault code is read, but the ABS light will not go out. It can only go out after using the foot brake after the driving speed reaches 7km / h.

Thinking for wheel speed sensor:

  • The common voltage output from ECU to magnetoelectric speed sensor is 2.5V, such as crankshaft, camshaft, wheel speed sensor, etc. the open circuit voltage of these sensors is 2.5V. Why is the wheel speed sensor of this car 5V? Relatively rare.
  • The most common vehicle speed sensors are crankshaft, camshaft and wheel speed sensors, which are divided into hall and magnetoelectric types. From the output signal, the magnetoelectric type output is positive Xuan wave signal and hall type output square wave signal. Today we mainly talk about magnetoelectric speed sensors.
  • Magnetoelectric sensor uses the principle of electromagnetic induction. It directly converts the mechanical energy of the measured object into electrical signal output. It does not need external power supply. It is a typical active sensor.
  • The system components are signal teeth and sensors. When the signal teeth rotate, they will cut the magnetic line of force of the sensor and generate AC voltage inside the sensor. The ECU calculates the corresponding speed of the components according to the output frequency of the signal voltage. The gap between the signal teeth and the sensor is 1mm ± 0.2mm. If the gap is too large or too small, it will affect the sensor signal.
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