Can anyone tell me if this is the speed sensor?

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Blazer811
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Re: Can anyone tell me if this is the speed sensor?

Post by Blazer811 »

white exec wrote:
08 Feb 2020, 20:29
Physically moving the needle could be an option.
If the instrument is just a voltmeter, driven from the ECU, then a simple adjustment pot on its input might give you (adjustable) correction, to dial back over-reading. Depends on how the instrument is built. Some even have an internal adjustment pot built in.
Pardon the ignorance Chris but what do you mean by “adjustment pot” and most importantly, how do I do?
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Re: Can anyone tell me if this is the speed sensor?

Post by white exec »

Re: the gearbox change by a previous owner, if a box with a different final drive (differential) ratio had been fitted, then a change in speedo behaviour could happen, if the speedo drive comes off after the gears, but before the diff/drive shafts.

If the box is ok, I'd leave it there (!), and just tweak the speedometer, if that's the only problem.

Re: the possibility of speedo adjustment, it could be that, inside the instrument, there is a small vriable resistor (potentiometer, pot) on the printed circuit board, that adjusts the needle reading. You would need to remove the instrument panel and look at the back of the speedo to see what's there.

In the absence of that adjustment, IF you are into electronics, it MIGHT be possible to reduce the instrument's reading by fitting a small veriable resistance, of suitable value, to achieve this. If you're not competent in working on circuit boards, this is best left alone.

QQ: You spoke about the needle being +10km/h. Is it always +10, across the scale, i.e. 20 shows 30, 40 shows 50, 60 shows 70, etc . . . . . or does the over-read get bigger than 10 at higher speeds ?

This is important to know, because the cure will be different for the two cases.
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Re: Can anyone tell me if this is the speed sensor?

Post by Blazer811 »

white exec wrote:
09 Feb 2020, 09:29
Re: the gearbox change by a previous owner, if a box with a different final drive (differential) ratio had been fitted, then a change in speedo behaviour could happen, if the speedo drive comes off after the gears, but before the diff/drive shafts.

If the box is ok, I'd leave it there (!), and just tweak the speedometer, if that's the only problem.

Re: the possibility of speedo adjustment, it could be that, inside the instrument, there is a small vriable resistor (potentiometer, pot) on the printed circuit board, that adjusts the needle reading. You would need to remove the instrument panel and look at the back of the speedo to see what's there.

In the absence of that adjustment, IF you are into electronics, it MIGHT be possible to reduce the instrument's reading by fitting a small veriable resistance, of suitable value, to achieve this. If you're not competent in working on circuit boards, this is best left alone.

QQ: You spoke about the needle being +10km/h. Is it always +10, across the scale, i.e. 20 shows 30, 40 shows 50, 60 shows 70, etc . . . . . or does the over-read get bigger than 10 at higher speeds ?

This is important to know, because the cure will be different for the two cases.
Yes Chris the speedo needle is reading +10km/h across the scale. Today I pulled the clear plastic cover slightly away from the instrument panel and with a wooden skewer stick I moved the needle downwards away from the 10km mark and it seems to have given me the solution I was after. It is now + 1km out according to the gps on my mobile and will test it at higher speeds tomorrow when I’m on the freeway.
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Paul-R
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Re: Can anyone tell me if this is the speed sensor?

Post by Paul-R »

Has the distance reading been accurate? From what you're saying I would think it has been.
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Re: Can anyone tell me if this is the speed sensor?

Post by white exec »

Blazer811 wrote:
09 Feb 2020, 12:32
. . . It is now + 1km out according to the gps on my mobile
That sounds good enough! Lucky to be able to to move the pointer on the shaft so easily.
=D>
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Re: Can anyone tell me if this is the speed sensor?

Post by Blazer811 »

white exec wrote:
09 Feb 2020, 16:52
That sounds good enough! Lucky to be able to to move the pointer on the shaft so easily.
=D>
Took it for a proper run and the speedo is +1km all the way up to 70km/h and then it’s start to increase to +5km from 80km upwards. So I’m wondering if a new speed sensor would be the go?
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white exec
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Re: Can anyone tell me if this is the speed sensor?

Post by white exec »

Very much doubt that is the speed sensor, but always possible.
Speed sensors, when they fail, tend to intermittently drop out, causing the speedo to flutter, badly under-read, or drop to zero. Can also cause a cruise control to stop functioning.

You could try a replacement - not too expensive, but suggest a genuine part from Citroen, rather than a cheap copy.
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Re: Can anyone tell me if this is the speed sensor?

Post by Paul-R »

Paul-R wrote:
09 Feb 2020, 12:45
Has the distance reading been accurate? From what you're saying I would think it has been.
?
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Re: Can anyone tell me if this is the speed sensor?

Post by Blazer811 »

Paul-R wrote:
11 Feb 2020, 10:27
Paul-R wrote:
09 Feb 2020, 12:45
Has the distance reading been accurate? From what you're saying I would think it has been.
?
Not sure on that Paul, but have that on my check list for tomorrow, once I establish this, I will let you know. Thanks for you help.
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Re: Can anyone tell me if this is the speed sensor?

Post by xantia_v6 »

The speed sensor sensor produces a fixed number of pulses per revolution, set by the mechanical design. It either works or it doesn't.
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white exec
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Re: Can anyone tell me if this is the speed sensor?

Post by white exec »

Not quite - the quality of the output signal can deteriorate, either through mechanical wear, or debris (despite being sealed units). Symptoms as described above.