UK Car Repair/speedo

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Question
hello
I've a 1999 Toyota corolla 1.6 gs, my problem is that when I turn on the car the needles on the dash such as petrol gauge and temp gauge rise up as the should , but recently the speedo rises up to between 5 and 10 mph, so that when I'm driving now I'm actually doing 5 - 10 mph slower than what my speedo is reading, what are the causes of this or what can I do to repair it,
thanks for any help


Dermot

Answer
The electric speedometer works from a pulse gotten from a magnet being passed by the ABS ring notches, or something similar. if the sensor has a bad earth, low input signal power, rattling loose connections, the speedometer can see pulses that aren't there.
Sometimes the electronic speedometer will jump when the notch is just close enough to nearly trigger the signal, and the car vibrating with the engine will make the needle jump violently as it gets a whiff of this 'noise'.

Also this phenomena can be caused from bad connections inside the speedometer as well.

Has the car been exposed to damp, maybe within 14 days before the fault developed?, that would make me think its more likely inside the car.

If its been through serious weather on the outside, I'd look to the sensors first.

If theres no indicator for in or out, go for the wheels first.


Obviously youre best just checking, cleaning - TLC the connectors from the speed sensors on the wheels, same with the dashboard connections, off, inspect for nasty green oxides, clean, reapir, rewire, splice.. make sure everything is wired together to start with.

Still bad speedometer reading?: part2

Oh myy..

give the dash a couple of smacks on the top - does it make a difference, loose connection kindof effect? - It'll be in the dash somewhere then or bad joints in the speedo.

Otherwise, youve got a short somewhere on the loom or an electrically noisy component on the car - voltage regulator, alternator, "equipment".. etc.  

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