Ford Speedometer Problems

by WilliamHanz
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Image by, courtesy of Nathan

The speedometer is an important part of the car engine as it indicates the speed of your vehicle while on the road. A faulty speedometer can cause major driving issues, which can lead to speed-related accidents or an unnecessary speeding ticket from the police. As with any brand of vehicle, Ford vehicles are susceptible to speedometer problems.


Most Ford vehicles are equipped with a Programmable Speedometer/Odometer Module (PSOM). The PSOM includes the odometer and the speedometer, which are electronically controlled by a programmable microprocessor. The module works by receiving speed signals from the Differential Speed Sensor (DSS) and converts the signal input to the standard 8,000 pulses per mile output.


The most common issues with the Ford speedometer are when it bounces back and forth continuously while the vehicle is being driven. Another problem that might arise is when the speedometer doesn't move at all. This indicates that the car's speedometer is dead.


Speedometer issues typically occur when major changes are made to the Ford vehicle. These include changing fuel types (from diesel to unleaded gasoline for example), and changing tires, as the vehicle's speed performance varies depending upon these two aspects. It is not uncommon then for you to experience a faulty speedometer after having had your tires changed, for example. The conversion constant needed to calculate your instantaneous speed is different and has yet to be determined.


If you think you are having problems with your Ford speedometer because of tire or fuel changes, the the best way to solve it is by resetting the PSOM. You can do this by pressing the SELECT button found on the upper right corner of the speedometer, then you select zero for the trip odometer. Next, you press the RESET button (typically on the upper left side of the speedometer), and once the trip odometer is displayed, you then press the SELECT button again to see the odometer value. It is also a must to change the speedometer's internal conversion constant if you have changed tire sizes because this will enable your speedometer to calculate your speed accurately.


Because the Ford speedometer is equipped in a full-device module, the only way to fix a broken speedometer is by complete replacement. The PSOM devices can be quite expensive because of their computer parts. Hence, it is important check out your speedometer's performance (as well as the odometer calculations) and provide the right conversion constants so that they will not only be able to provide correct calculations, but also avoid incompatibility problems with any new changes made to the vehicle.

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