Speedometer calibration ?

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jkirkebo

Well-known member
Joined
Jun 18, 2010
Messages
400
Location
Fredrikstad, Norway
My speedo reads 8% high. Avg.speed is correct as is driven distance. Does anybody know if it is possible to calibrate the speedometer by using the Consult-thing at the dealer ? I would really like a 100% correct speedometer...
 
8% is within the federally mandated error range of +/-10% - probably won't be a warranty item if they bother to fix it at all. I'd learn to live with it since it's basically erroring in your favor anyway. I'm also curious as to how you verified the error margin...

You will usually find that speedometers read high since nobody wants a lawsuit over a speeding ticket. "But officer, my speedometer said I was going 55, not 60!"
=Smidge=
 
I think +/- 10% is incorrect.
Where did you get that, or is it a guess?

I think the law requires the speedometer to NOT read low (in OEM configuration, tire pressure, etc.), so the DISPLAYED speed is usually about 2% over the internally "calculated" speed.

If you are 8% high, that wiuld seem unusual, and your tire pressure and temperature might be low?

Using the hidden "Calibration" screens (with Audio power off, quickly press: Map, Map, Map, Audio (on), Audio (off), Map).

One of the screens shows the "wheel" and GPS derived speeds (100.0 kph (shown as 1000) = 62.5 mph) and the LEAF will "usually" DISPLAY about 65 mph in the dash "eyebrow".

It might also indicate if the wheel (or motor RPM) derived speed differs from the GPS derived speed.

I am not aware of any way to change the Speedometer "offset", or recalibrate the internal speed. Since the LEAF has the GPS-derived speed available, it COULD be self-calibrating, and carefully reporting 2% high. But, if your car is actually showing 8% high, then it would appear that your car is NOT self-calibrating.

Of course, running larger diameter rims or higher-profile tires would make your car go faster than indicated by the RPM-derived speed.
 
It would seem very unusual for the speed to be high and the distance to be correct. They are usually derived from the same signal.
 
garygid said:
The DISPLAYED speed is deliberately shown higher than the internally-used speed.

I assume you are speculating and haven't reverse engineered the firmware in the dash display?

I've never worked with an ECU that has held two different speeds. That's not to say it's not possible, but I haven't seen it. The Speed in the ECU is always the speed that is displayed.
 
turbo2ltr said:
garygid said:
The DISPLAYED speed is deliberately shown higher than the internally-used speed.

I assume you are speculating and haven't reverse engineered the firmware in the dash display?

I've never worked with an ECU that has held two different speeds. That's not to say it's not possible, but I haven't seen it. The Speed in the ECU is always the speed that is displayed.

My average speed and distance reads correct. If I accelerate to 80kph, set the cruise control and reset the avg. speed, it will show ~75kph after a while. I have to set the cruise control to 86kph for the average speed to read 80kph.

I have verified that the average speed is the correct one, by external GPS and radar speed displays along the road.

My tire size is the original one. The car seems to know the correct speed but still displays 8% high.
 
In the LEAF, I have checked the display against the "calibration" screen.

The odometer is required to be "correct", so a "correct" internal speed can usually be derived. However, if a car is not making any "efficiency" calculations, a "real" speed might not be required internally.

I do not know if the "speed" is required for smog checking. Perhaps just the RPM is required?

However, since the speedometer is required to be "not low", it is standard practice (required in many countries) for the speedometer to display a higher value.

For example: The ScanGaugeII for the 2010 Prius shows the "real" (internal) speed, but the car's speedo displays a higher value.

In the LEAF's OBD data, I see what appears to be RPM, but I have not yet found distance or an explicit "speed" (that I could recognize).

Have you found tire pressure or battery pack temperature in the OBD data?
 
jkirkebo said:
I have verified that the average speed is the correct one, by external GPS and radar speed displays along the road.
GPS is only as accurate as its own current accuracy and sample rate. Roadside radar speed displays usually display low due to using older RADAR technolgy and their positioning/aim on the road. Systems like LIDAR that law enforcement use are much more accurate and would probably be better to test your speedometer. Know any cops? :D
 
What is "GPS own current accuracy"?

+/- 50 feet out of 8000 miles?

100 feet out of 8000 x 5000 is one part in 400,000.

Sample rate in typical handheld GPS units is about 1/second.
In some cars perhaps 2 times per second.
 
DarkStar said:
jkirkebo said:
I have verified that the average speed is the correct one, by external GPS and radar speed displays along the road.
GPS is only as accurate as its own current accuracy and sample rate. Roadside radar speed displays usually display low due to using older RADAR technolgy and their positioning/aim on the road. Systems like LIDAR that law enforcement use are much more accurate and would probably be better to test your speedometer. Know any cops? :D

Still, when external GPS, radar displays and the avg.speed indicator ALL agree on the speed (to better than +/- 1kph) and the speedometer displays 8% higher, I tend to believe the former three...
 
turbo2ltr said:
It would seem very unusual for the speed to be high and the distance to be correct. They are usually derived from the same signal.
FWIW, you and others here might find this old article from 2002 interesting: http://www.caranddriver.com/features/speedometer-scandal" onclick="window.open(this.href);return false;. There's also an easy to miss .pdf link from that article at http://www.caranddriver.com/var/ezflow_site/storage/original/application/1e1b33f85f31df61e4830f32f82a5a71.pdf" onclick="window.open(this.href);return false;.

There's some discussion of UNECE (!) regulations at http://priuschat.com/forums/gen-iii-2010-prius-technical-discussion/77291-speedometer-error-about-1-mph-some-evidence-2.html#post1282138" onclick="window.open(this.href);return false;.
 
The internal speed and distance values are as accurate as the car can manage (and circumstances like tire size and pressure permit).

It is only the DISPLAYED-to-the-driver speed that is "boosted".

So, the display-only speedometer "lie" does not affect the odometer or other internal speed or distance calculations.
 
I received a speeding ticket a few years back.

Speedo showed 55mph but I was actually going 68mph (freeway posted max was 55). It was that much out of wack.

I went to a Speedometer shop for calibration readings for proof to take to court to fight the ticket.

Judge said, "You aren't required to have a speedometer in the vehicle, you are just required to drive the speed limit."

I lost the case :evil:
 
jkirkebo said:
My average speed and distance reads correct. If I accelerate to 80kph, set the cruise control and reset the avg. speed, it will show ~75kph after a while. I have to set the cruise control to 86kph for the average speed to read 80kph. .

I'm not sure if this is a good method. Why would it know the seemingly correct average after the reset at 80kph indicated on the display?

But, regardless, something doesn't add up. Have you tried the calibration settings in the service menu?

(Audio Power off, Map, Map, Map, Audio Power, Audio Power, Map)
 
Man! You guys crack me up with your "nit-picking". I mean, it must be frustrating to try to pick the fly-s$$T out of the pepper. Why don,tcha just drive and enjoy.... :roll: :roll: :roll: :roll: :roll:
 
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