Vehicle speed sensor. Free Technical Library article

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Vehicle speed sensor (2112-384301)

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Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic fuel injection

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The vehicle speed sensor (DSA) is designed on the principle of the Hall effect and outputs a frequency-pulse signal to the controller. The frequency of the signal is directly proportional to the speed of the vehicle. The controller uses this signal to control the engine idle and, through the idle speed controller, controls the air supply bypassing the throttle. DSA generates approximately 6004 pulses for every kilometer traveled by the vehicle. According to the time interval between pulses, the controller determines the speed of the vehicle. In addition, this signal can be used by the speedometer installed on the instrument panel. The appearance of the vehicle speed sensor is shown in photo 1.

DSA is installed on the gearbox (see photo 2) on the speedometer drive mechanism.

It is dismantled after (with the ignition off) disconnecting the contact connector and the speedometer drive cable (if installed) by unscrewing the sensor from the speedometer drive. Installation of DSA is carried out in the reverse order of dismantling. In case of malfunctions in the DSA connection circuit, the controller enters the code "24" into the RAM and lights the "CHECK ENGINE" lamp, thus indicating the need for diagnostics. One of the pronounced symptoms of a malfunction of the speed sensor is the stop of the engine at X.X. when the vehicle is rolling. However, one should not forget that a similar situation can occur with temporary malfunctions of the mass air flow sensor (MAF), but the "CHECK ENGINE" lamp, in this case, does not always light up. On this basis, it is possible to preliminarily judge which particular sensor is out of order. Checking the performance of the DSA should begin with the presence of grounding on pin "3" and supply voltage (+12V.) on pin "1". Checking the pulse signal on pin "2" should be carried out with the rotation of the drive wheels at a speed of at least 5 km / h. I recommend measuring with a digital multimeter or an oscilloscope. To check the "1" and "3" contacts of the DSA, the use of continuity is allowed. Typical symptoms of a malfunction of the speed sensor or its circuit include stopping the engine when shifting gears and coasting, errors in the speedometer readings.

Most often, the failure of the DSA is associated with the operation of the speedometer cable. If this cable has any burrs, breaks on its surface, or its rotation in a protective sheath is simply difficult, this can lead to failure of the speed sensor (see photos 3 and 4). In addition, often because of this reason, the speed sensor fails precisely at high speeds. In photo 3, the metal rod that transmitted the rotation melted the plastic and, as you can see in the photo, just fell out. On the other hand, the speedometer cable simply broke its seat and, accordingly, ceased to be fixed in it, which led to the failure of the normal operation of the speedometer (see photo 4). Since the sensor circuit was not damaged, the "CHECK ENGINE" lamp did not light up due to the absence of fixed errors in this circuit. In this case, the problem was solved by simply replacing the speedometer cable and speed sensor with new ones. To avoid this situation, while the speedometer cable is in good condition, it should be lubricated with engine oil.

Photos 5, 6 and 7 show another version of the speed sensor (301.3843).

Publication: cxem.net

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