The speedometer not working?

The instrument which informs you and let you know how fast your car is moving is speedometer.
There are generally two types of speedometers.
In one type of car the speedometer head is connected to the output shaft of the transmission by means of flexible speedo cable. Which is attached to the pinion gear in the transmission.
In other type of cars the speedometer and odometer are driven by flexible cable that is attached to one of the cars wheel, usually the left hand front wheel, is where this cable is connected.
The noise from speedometer very much indicates towards the faulty speedometer or end of speedometer life is very near and it needs inspection.
Inspecting the speedo meter cable helps, many a times this cable gets loose or shorted from its connection and causes the problem.
Now a days digital speedometers are introduced.
In these type of speedometers, there is a sensor on the car’s rotating shaft. Also, the rotating shaft has a magnet joined to it and is placed besides a magnetic sensor. A tiny electrical current, in form of a pulse, is produced whenever the rotating shaft passes the sensor. This pulse rate is calculated by a little computer and sent to the dial where you can see the car’s speed.
On digital speedometer, f it stops working then the VEHICLE SPEED SENSOR has to be replaced.
On old type speedo, the problem is speedo relates to faulty speedo cable.
Speedometer Cable Replacement
Take out the engine cover and doghouse to remove the speedometer cable from your car. Take out the bolt from under the dashboard, so that you can easily access the old speedometer cable. Also remove the nut on the rotating shaft and pull the speedometer cable out through the passage. Remove the clamps present on the transmission and engine compartment. Once you have removed the old speedometer cable from your car, you need to replace it with a new one.
Speed Sensor Replacement for Front Wheel Drive Vehicles
You will find the speed sensor behind the engine above the trans-axle. Take out the connecting hose, air cleaner and electrical connector from above the sensor. With help of a 10 mm socket, take out bolts keeping the sensor in place. Simply twist the sensor to take it out. Fix the new sensor in place and tighten bolts around it. Attach back the hose, air cleaner and the electrical connector on to the sensor.
Speed Sensor Replacement for Rear Wheel Drive Vehicles
You will find the speed sensor on the driver’s side behind the transmission. Raise the vehicle up from the driver’s side and put a jack stand below to hold it there. Disconnect electrical connectors present on the sensor and take out bolts keeping the sensor in place, using a socket. Take out the sensor carefully and fix a new one in its place. Attach the electrical connector to it and tighten it.
On old style speedo, the speedometer cable fits into the metal funnel of the housing, so feed the cable into the housing slowly to avoid cable kinking or getting damaged.
In some digital speedometer cases replacing the speed sensor does no helps, in that case the speedo cable to the module has to be checked.
Here’s how the system works:
If you don’t have ABS the vehicle speed sensorsends electrical pulses generated by a tone ring directly to the body control module ( BCM), when then measures how fast it receives these pulses and translates this into a vehicle speed reading and sends it to the PCM (Engine computer). The PCM then tells the speedometer what speed to display.
If you DO have ABS, the ABS Module measures the vehicle speed, then sends it to the Body control module, which then sends it to the PCM, which then tells the speedometer what to read.
If you had a communication loss between the modules, the speedometer is programmed to read the last received speed for six seconds, and then if it still isn’t being told what to do, should drop to ZERO.
If you have ABS and it was getting a vehicle speed deading of 18MPH, but the wheel speed sensors were reading a higher speed, it would turn on the ABS light, so if you have ABS I think most likely the Speedometer assembly itself it bad. (As long as the ABS light isn’t staying on).
If you don’t have ABS, then it’s still quite possible you have a bad Speedomoter assembly, but there’s also the possibility of the Body Control Module doing goofy and glitchy stuff, but it’s not very likely at all. I would smack above the speedometer on top of the dashboard while you are driving.. if it comes to life and starts working you know that’s the case.
It is extremely important, as without a functioning speedometer you have no true way of determining your current speed (at least until a police officer pulls you over and shows you the radar reading). Because of this, if you believe the speedometer in your vehicle is not displaying an accurate speed you need to troubleshoot the device in order to correct any problems that may be occurring.






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