Faults in Speedometers and how to fix them.

Forums › Transport (cars, bikes and boats) › Faults in Speedometers and how to fix them.

RUKI

1402 posts

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#311203 22-Dec-2023 20:11

Statement:
1) speedometers (aka combination meters or instrument clusters) are reliable electronic devices which rarely fail on its own.
2) many modern Japanese imports do not have selection of English in them. Some can be converted but some cannot.

FAQ: my car is going about 110kmh according to speedometer, but GPS shows 100. Is it faulty?
Answer: it is not faulty, it's factory design. Speedometers in Toyota, Honda, Mazda or Nissan will display more than your actual speed by certain non-linear coefficient. FYI - contrary to general belief - it is not 10%. It will show, for example 170kmh when you drive 160 as tested with standard Toyota' calibration procedure at 40, 80, 120 and 160kmh on the bench.

Sharing experience. The faults I observed:
1) faulty LED back light or warning light in Toyota Hybrid Fielder, Noah, Nissan Leaf. Fix: in some - LED replacement, in some - swap for working cluster from wreck and transfer all data accross. Note: transfer is important as data may contain vehicle configuration which could be different on the same cluster part number, e.g. Toyota Fielder.
2) wrong configuration speedometer (somebody done something wrongly) E.g. Prius ZVW30. Fix: program stock config
3) Leaf 40kWh and Kicks speedometers - ODO is frozen (traces of 3-rd party soldering inside). Stock back up reprogramming did not help. Fix: replacement for working one from wreck
4) completely dead black display in Prius Taxi after 500000kms. PCB is multilayer - cracks in the middle layer. Non fixable. Replacement. Data extracted from the dead and transferred to the donor from wreck.
5) Corolla Hybrid 2017. All needles down, not moving. Non fixable. Replacement.
6) Toyota Fielder 2017 dead LCD, burnt components on board - cluster replacement.
7) dead black screen Honda 2022 - non fixable. Stock reprogram did not help. Replacement.
8) Lexus IS350 - LED failures and LCD failures. They tried to change LEDs for different colors and damaged clusters. Suggested to source donor from wreck and transfer data.

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1402 posts

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#3174683 22-Dec-2023 20:16

Correction: FAQ: car' speedo shows 110kmh but I am going 100 according to GPS.

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freitasm

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Geekzone

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#3174699 22-Dec-2023 21:29

I see the same with my VW Golf. Speedometer shows 110 KM/h, GPS and road signs show 100 KM/h.

In our case it seems to be a constant 10% - travel at 55 KM/h while road sign shows 50 KM/h, or travel around 88 KM/h with GPS/sign showing 80 KM/h.

eracode

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#3174700 22-Dec-2023 21:33

There’s a lot of experience and detail there but I’m not sure what your point is. Simply: Imported Japanese cars’ speedos over-read/report?

Sometimes I just sit and think. Other times I just sit.

k1w1k1d

1519 posts

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#3174751 22-Dec-2023 22:05

I believe the NZ rule for speedos is the indicated speed can be up to 10% +4kph of actual speed. A car with the speedo reading 100kph can actually be travelling at only 87kph.

Speedo is not permitted to read low.

My work Toyota shows 100kph at 94kph, so I normally cruise at 106kph on the speedo. I also have a GPS app on my phone that I often use on trips.

Wheelbarrow01

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Chorus

#3174755 22-Dec-2023 22:28

k1w1k1d:

A car with the speedo reading 100kph can actually be travelling at only 87kph.

This drives me insane when I am stuck behind one. Actually one is ok as I can usually get past, but when I'm 3rd or 4th in a train of cars, and there's no sufficient gap between the cars to pass them individually, and the cars in front of me are content to just sit behind the leader while I lose the will to live.... Then queue the passing lane and all of a sudden it's 120kph all round. Exactly 120kph. In both lanes. Side by side. So no-one ends up getting past. Then back to 87.

It's the reason I set out for our bach at 4 or 5am these days, so I pretty much have the road to myself. Ah the serenity...

Mehrts

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#3174815 22-Dec-2023 23:37

Inconsistently slow drivers are the worst. Slight bends and they're on the brakes while on a smooth straight they're at 100kph. Go to pass on a passing lane and the pricks speed up even more! If only they could experience the frustration they cause to other road users with this behaviour.

Constantly slower ones, such as trucks etc are fine because they're predictable and usually allow ease of passing.

RUKI

1402 posts

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#3174819 23-Dec-2023 00:25

@eracode - the point is - Instrument clusters are usually not faulty except those Prius which travelled way too long or some unexplained damage.
But when somebody tries something they have no idea about - the end result could be an expensive replacement. The message here is simple as with any IS/IT change - what is your back up /back out plan if you damage it?
Last week owner of the ZE1 Leaf sent me a photo of their cluster with lost segments on the left side and non-erasable DTC. That happened straight after incompetent attempt by somebody to change the language. They are chasing those who did it for now...

One positive outcome was with replacing Lexus ISF pre-restyle (back light fault) cluster with cool looking restyle cluster - owner sourced one brand new from Japan, I confirmed on the bench - pinouts to be exactly the same, converted it to English and transferred data accross.

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gregmcc

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#3174824 23-Dec-2023 06:07

Those with factory fitted navigation systems - ever wondered why the speed from this isn't one of the displayed properties? - this is the reason, can't have GPS saying one speed and the speedometer showing a different one.

Personally I have a separate GPS and use this for my speed reference.

SCUBADOO

192 posts

Master Geek

#3174902 23-Dec-2023 08:35

Our inbuilt Suzuki Grand Vitara Garmin entertainment head unit clearly displays the GPS derived speed. The typical 5km/h speedometer difference is obvious.

freitasm

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Geekzone

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#3174924 23-Dec-2023 09:39

SCUBADOO:

Our inbuilt Suzuki Grand Vitara Garmin entertainment head unit clearly displays the GPS derived speed. The typical 5km/h speedometer difference is obvious.

Please send your car for repairs. Your GPS will be removed.

alasta

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#3174927 23-Dec-2023 09:55

How accurate is GPS as a speed measure in a car?

As a runner, I have my sports watch set to show my speed over a rolling average kilometre because the instantaneous speed measure tends to fluctuate and lag a bit.

RUKI

1402 posts

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#3174931 23-Dec-2023 10:09

@gregmcc good question.

Navigation Head Units are getting GPS signal but not sending speed signal to the Combination Meter. Head Units though send clock signal (and other info, like music played or "next turn" ) to the speedometer.
When I reprogram Time Zone in Nissan Leaf' Clarion QY82xx /86xx - it sends correct time to speedometer, but does not send speed.
In some JDM Hondas 2018+, depending on specs - Head Unit sends clock signal - I have intersepted corresponding CAN-bus messages. When people replace such head unit with aftermarket one - they loose clock display in speedometer. Currently not fixable.

The other dialogue between head unit and speedometer in latest JDM Hondas is so called SOS - emergency breakdown assist message I have couple of such speedometers 2022.in my LAB but do not have head unit yet to play with to read SOS related CAN-bus. Assumption here is that after replacing such head unit speedometer may display "SOS system malfunction" as it will be missing required signals... Honda NZ Service Department - do not have tools/processes in place to "up program" features which are not present in NZ new specs vehicles. Same with Toyota and Mazda official dealerships. Not in their SOP.

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SCUBADOO

192 posts

Master Geek

#3174946 23-Dec-2023 10:27

alasta:

How accurate is GPS as a speed measure in a car?

As a runner, I have my sports watch set to show my speed over a rolling average kilometre because the instantaneous speed measure tends to fluctuate and lag a bit.

Even my now 20 year old hand held Garmin GPS claimed in the specs 0.328 ft./sec. when in a steady state straight line.

That equates to 0.36 km/h.

The current GPS satellite network must have well and truly improved on that over the years.

mudguard

2113 posts

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#3174980 23-Dec-2023 11:39

alasta:

How accurate is GPS as a speed measure in a car?

As a runner, I have my sports watch set to show my speed over a rolling average kilometre because the instantaneous speed measure tends to fluctuate and lag a bit.

A car is probably more accurate than a sports watch running. The satellite antenna is probably much bigger, fewer overhead obstacles for a car, and consistent recording intervals.
Whereas jogging, you might run up a hillside with switchbacks, and unless you've set your recording intervals to say 1 second (I think that's the shortest my Garmin does) you might chop out big chunks of your run.

We see it all the time with mountainbiking, people using phone based Strava, vs dedicated GPS devices. I have a wheel sensor on my bikes so that deals to GPS clipping, the result my rides tend to be longer than someone else I'm riding with just using GPS.

As for cars, well as we go to more and more screens a fewer analogue dials I guess there's a risk. I don't see it being a huge issue. I'm a Honda fan but there are certain models that I'd like to own but haven't. As the fun VTEC models could come with integrated satnav and climate control that was all in Japanese and not straightforward to change. Accord Euro R for those that care.

shk292

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#3174982 23-Dec-2023 11:43

It's a minor irritation that Google maps on Android Auto or Carplay doesn't show GPS speed - I guess for the same reason as the inbuilt nav systems don't

Presumably if you displayed speed from the OBD port, it would be true not "fudged" to over-read

Presumably Nissan Leaf speedos all over-read badly because they always seem to drift along at 85-90 on a clear motorway

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