Symptom: a Santana 2000GSi sedan, driving 80,000 km, the car is equipped with MK20-I anti-lock braking system, this car ABS fault light, the owner open to the repair shop for maintenance.
    Failure analysis: First, with the yuan power eye fault diagnostic apparatus to read the fault code, the ABS system to detect, display "00290", for the left rear wheel speed sensor G46 failure. Under normal circumstances, the following three cases will lead to ABS system such a failure:
    (1) When the speed exceeds 10km / h, no speed signal is transmitted to the ABS control unit.
    (2) When the speed is greater than 40km / h, the speed signal exceeds the tolerance value.
    (3) The sensor has a recognizable circuit breaker or a positive pole, ground short circuit fault.
    Based on experience, the following items should be focused on:
    (1) Line connection between the wheel speed sensor and the ABS control unit.
    (2) wheel speed sensor and ring gear installation gap, installation location and dust or impurities contaminated by the situation.
    (3) whether the wheel bearing clearance is too large.
    (4) The sensor itself is faulty.
    In the car troubleshooting process, the first did not rush to check the wheel speed data. The engine idling operation, select the reading data block function, into the 001 display group, with a lift machine to rise, observe the display data.
    When the wheel is at rest, the display area shows 0km / h. Turn the left rear wheel by hand, and the third display area shows 9km / h. And then turn the other wheels, observe the corresponding display area, found that basically the same. Put down the vehicle, use the fault diagnosis device to clear the fault code. ABS warning lights go out, road test everything is normal.
    Read the measurement data block function with the diagnostic device, enter the display group 002, observe the third display area left rear wheel speed. Whether in acceleration, deceleration, braking, low speed or high speed, its value and the other three wheel speed is basically the same. ABS warning light is not lit, the brake can also feel the ABS system at work, the failure did not appear. Because there is no fault, they are ready to let the owner pick up the car.
    At this point, the fault again appeared. When the vehicle is idle, the fault warning light is on. Code detection and produce left rear wheel of the occasional fault code. According to the situation of the car inspection, there is only one possibility, that is, left rear wheel speed sensor and ABS control unit between the instantaneous short circuit or open circuit. According to the circuit diagram for inspection, it was found that the ABS control unit 25 pin plug 10 pin has a slight corrosion. After cleaning the repair plug, clear the fault code. Owners driving more than 2000 km did not appear the original failure.
   When asked the owner to know, cleaning the vehicle, often with high pressure water rinse engine compartment, due to high pressure water splashed into the ABS control unit connection point, 25 pin plug 10 pin is corroded, resulting in an instant open circuit situation. This fault is a soft fault, the probability of failure there is a great random, the general use of multimeter is not easy to detect, and only in the event of failure, can find the cause of the malfunction, find the root cause, the right medicine, the troubleshooting.