Vehicle Speed Sensor

Fuel supply rate varies depending on car speed. If driver pushes accelerator pedal deeply at low speed, the situation may be decided as requiring higher output. On the other hand, if at high speed, it may be decided as requiring high speed running.
There are two types of speed sensor:

• Lead switch type sensor is installed in speed meter.


• Hall type sensor is installed at trainable speed meter driven gear.

Lead switch type sensor generates 4 pulse signals per a revolution of output gear. Lead switch interrupts 5V power supply from ECM to convert generated speed signal to pulse signal. Then ECM receives the pulse signal, which will be used for idling speed adjustment.Hall sensor type finds whether car is in idling or running. When current flows it receives 0.5V, when Hall sensor does not operates it receives 12V signal, to detect car speed. To say it has the role to detect load.
In particular, in case of A/T cars, engine may go off when the car stops if car speed sensor is faulty, and therefore more careful checking is required. In addition, Hall sensor types may have different pulse number.

• If there is a circuit-break or short at speed sensor wiring, engine may go off when decelerating the car to stop. Therefore connector connection and short circuit in wiring or circuit break must be checked.


• For Speed sensors of lead-switch type or Hall Effect, Therefore it is required to analyze signal using oscilloscope.


• Check if frequency, period, and specified voltage value occur normally.


• Check if frequency rises in proportion to car speed variation.


• Check if input voltage and grounding are maintained normally at on and off condition.


• Speed sensor input voltage is 5V for lead-switch type and 12V for Hall sensor type. AS car speed rises, speed sensor output frequency goes up. Voltage drop at ground shall be less than 400mV. If not then check the speed sensor and ECM for defective grounding.

• Engine malfunction during idling.
  
• When starting car, or when decelerating car to stop, car lingers instantly or engine goes off.


• Poor acceleration of engine.

You can check the sensor actual value and status by AutoHex Automotive Scanner under the supported car brand and according to engine type.

AutoHex II

Autohex II For BMW

AutoHex II For Kia and Hyundai

AutoHex stand alone

Mercedes Technical Info