Can anyone tell me if this is the speed sensor?

[white exec]

That's it.
The instrument is just a voltmeter, so possible that it is over-reading. If the reading is steady and consistent, it could even be just a matter of realigning the pointer - a delicate job, usually.
Someone here may have come across the fault before. Do post your VIN, which could help.

[furriegurrie]

Do you have the correct tires fitted to the car? Different size than factory spec will also influence the speed indicated vs actual speed.

[Huskyxantia]

Hi all,Hi all, I have a 2004 Berlingo 1.4i van and the speedo shows around 10kmh more than what I am actually doing. I have searched high and low for the speed sensor unit and this is the only thing that I’m thinking it could possibly be.

If it isn’t, can someone please point me in the right direction.

Many thanks

Sure is

[Huskyxantia]

Do you have the correct tires fitted to the car? Different size than factory spec will also influence the speed indicated vs actual speed.

If the gear box is the same but a differnt model then the sensor will be the same wheel size can make a difference to speed smaller wheels make needle lift quicker and vice versa , that's my experience a few years back, if it makes sence

[white exec]

What are you checking the speedometer reading against? Satnav/phone or similar?

For a definitive check, your local police may be able to tell you where their "measured mile" is located - usually marks on a stretch of road, or posts at the side. Drive it at steady indicated 60mph, and see if it takes 60s. Good, old-fashioned stuff.

Common for speedos not to start at 0mph, because of errors below 5?10mph. Should be reasonably accurate (±10%) from 20mph upwards. Worth checking the tyre size - often labelled on an A-pillar.

[Hell Razor5543]

As I understand it vehicles can have an error of 10% OVER the actual speed of the vehicle, but 0% UNDER the actual speed (although in the UK the speedometer can legally show 10% + 6.25MP/H over the true speed, but not above this). This means that you should never be unknowingly speeding.

https://www.thecarexpert.co.uk/how-accu ... eedometer/

[xantia_v6]

It is just the way they build these cars. The German and Japanese manufacturers seem to manage to fit speedometers that are accurate to a km/h or two, but PSA can't.

As a point of reference, our 308 over-reads by 4 km/h at 50, 6 kn/h between 60 and 100 km/h. You just learn the correct indicated points for each speed limit.

You can't fix it by altering the gearing of the speed sensor, as the engine ECU is programmed with the ratio of engine RPM to wheel RPM for each gear and gets upset if the ratio appears to be wrong. Maybe the needle on the speedometer could be moved, but that does not help if there is also a digital speed readout.

[Hell Razor5543]

I have found that the Citroen C5 Mk1 has a VERY accurate speedometer. Compared against a Sat Nav both my previous C5 and my current C5 are almost exactly spot on.

[white exec]

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.

[myglaren]

I have found that the Citroen C5 Mk1 has a VERY accurate speedometer. Compared against a Sat Nav both my previous C5 and my current C5 are almost exactly spot on.

I'll second that James. I was quite surprised at how accurate it is and that is over two cars.

[Hell Razor5543]

As I understand it the C5 Mk1 uses the ABS sensors for the speedometer, and not a gearbox sensor (although I could be wrong).

[white exec]

If the error is always the same figure, eg +10km/h, across the scale, then reposition the needle.
If the error is a % over-read - eg 22 at 20, 44 at 40, 77 at 70 - then you need to attenuate the voltage driving the meter coil/needle.

If the latter, and you are not able to open up the instrument to examine/adjust, then Speedy Cables, in S.Wales, will correct this for you if you tell them the exact % over-read.

These instruments work by taking a frequency (from gearbox sensor or ABS ring), and converting it linearly to a voltage, which the speedo displays.

[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.

[Paul-R]

Has the distance reading been accurate? From what you're saying I would think it has been.

[white exec]

. . . 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.