Beeping when over the speed limit (misidentification of speed limit).

Mildly_Miffed

flaneurs_lobster said:

Forgive my ignorance of these things - is the car detecting/deducing the speed limit by using a camera to read road signs / look for street lights or are the limits predefined, downloaded and applied by GPS like Waze etc.

It could be either.

Some are GPS-mapping, tied to DashboardDoris's satnag database. Others are camera-led. Some use both.

https://etsc.eu/intelligent-speed-assistance-isa/

If you look in the upper/centre of the windscreen, behind the mirror, there's a big fat slab of plastic.

That contains a bunch of sensors for all sorts of ADAS (Advanced Driver Assistance Systems) tech, from daylight and rain sensors for headlight and wiper auto modes, to cameras for speed limit detection etc. If you have adaptive cruise, the radar for that is probably in the grille/bumper, but might be up there, too.

If you need the windscreen replacing, the sensors and cameras usually need calibration afterwards.

The "it reads 30 as 80" anecdote will be camera - and the sign needs a good clean...

droopsnoot

flaneurs_lobster said:

daveyjp said:

Search owners club sites and see if there is a hack for defaulting the system to off, or whether it can be done via the OBD port.

Do you think forgetting to re-enable will become a Mot fail, if the thing is now mandatory? 

Unless it throws a warning light or sound while it's disabled, that would be quite a difference to the MOT test as it would require a road test to confirm whether or not it's working.

flaneurs_lobster

droopsnoot said:

flaneurs_lobster said:

daveyjp said:

Search owners club sites and see if there is a hack for defaulting the system to off, or whether it can be done via the OBD port.

Do you think forgetting to re-enable will become a Mot fail, if the thing is now mandatory? 

Unless it throws a warning light or sound while it's disabled, that would be quite a difference to the MOT test as it would require a road test to confirm whether or not it's working.

Isn't the whole point of turning the thing off to avoid a warning light/sound?

Mildly_Miffed

droopsnoot said:

flaneurs_lobster said:

daveyjp said:

Search owners club sites and see if there is a hack for defaulting the system to off, or whether it can be done via the OBD port.

Do you think forgetting to re-enable will become a Mot fail, if the thing is now mandatory? 

Unless it throws a warning light or sound while it's disabled, that would be quite a difference to the MOT test as it would require a road test to confirm whether or not it's working.

...or fault-code reading.

IF it ever becomes part of MOT (and remember that cars that have it compulsorily fitted won't require MOTs until summer 2027), then it will likely be "if there's a warning light, it's a fail."

OBD reading is not part of the MOT, although OBD *can* be used for temperature readings for emissions testing. At least, not YET. But it's coming.

However, ADAS is not part of the standardised OBD fault codes - it's manufacturer specific, so the diagnostic kit required would be much more complex and expensive. Yes, most garages probably already have something capable. But they'd require APPROVED kit specifically for the MOT bay.

Herzlos

droopsnoot said:

flaneurs_lobster said:

daveyjp said:

Search owners club sites and see if there is a hack for defaulting the system to off, or whether it can be done via the OBD port.

Do you think forgetting to re-enable will become a Mot fail, if the thing is now mandatory? 

Unless it throws a warning light or sound while it's disabled, that would be quite a difference to the MOT test as it would require a road test to confirm whether or not it's working.

You can only mute it temporarily for a single journey. It'll reset back to being on whenever you turn the car on so it shouldn't make a difference to an MOT. 

If you modify the car to disable it permanentally, then it'd likely be an MOT fail. But I'm not sure if it's something they'd be able to identify if there wasn't a warning light or fault code. 

NBLondon

Mildly_Miffed said:

flaneurs_lobster said:

Forgive my ignorance of these things - is the car detecting/deducing the speed limit by using a camera to read road signs / look for street lights or are the limits predefined, downloaded and applied by GPS like Waze etc.

It could be either.

Some are GPS-mapping, tied to DashboardDoris's satnag database. Others are camera-led. Some use both.

My 2025-built Peugeot allegedly does both.  If it can't see a sign at startup - it takes the satnav value.  After that, it switches depending on which of those last changed.   In 3 months, it's got it wrong a couple of times - picking up a stray sign and assuming it was a repeater.  One of those told me the speed limit was 96mph, so there doesn't seem to be a sense-check in the processing.

prowla

wongataa said:

flaneurs_lobster said:

Forgive my ignorance of these things - is the car detecting/deducing the speed limit by using a camera to read road signs / look for street lights or are the limits predefined, downloaded and applied by GPS like Waze etc.

The car reads the road signs.

But it can misread them, for example if you approaching a bend on a main road where there is a turnoff which has a sign for its speed limit.

I had this happen on the weekend: I was going along a 40 or 50 main road and there was a junction into a road with a 30 sign.

user1977

prowla said:

wongataa said:

flaneurs_lobster said:

Forgive my ignorance of these things - is the car detecting/deducing the speed limit by using a camera to read road signs / look for street lights or are the limits predefined, downloaded and applied by GPS like Waze etc.

The car reads the road signs.

But it can misread them, for example if you approaching a bend on a main road where there is a turnoff which has a sign for its speed limit.

I had this happen on the weekend: I was going along a 40 or 50 main road and there was a junction into a road with a 30 sign.

It also can't read any context e.g. a 20 limit which only applies when the schooltime flashing lights are on, the 50 limit on the single carriageway bits of the A9 which only apply to HGVs, etc.

flaneurs_lobster

user1977 said:

prowla said:

wongataa said:

flaneurs_lobster said:

Forgive my ignorance of these things - is the car detecting/deducing the speed limit by using a camera to read road signs / look for street lights or are the limits predefined, downloaded and applied by GPS like Waze etc.

The car reads the road signs.

But it can misread them, for example if you approaching a bend on a main road where there is a turnoff which has a sign for its speed limit.

I had this happen on the weekend: I was going along a 40 or 50 main road and there was a junction into a road with a 30 sign.

It also can't read any context e.g. a 20 limit which only applies when the schooltime flashing lights are on, the 50 limit on the single carriageway bits of the A9 which only apply to HGVs, etc.

In this age of essentially unlimited computing power available in your pocket, pretty sure there's enough smarts in your motor to work out what some flashing lights and the word "SCHOOL" mean WRT speed limits.

Ditzy_Mitzy

I suppose you could purloin a national speed limit sign from somewhere, attach it to a selfie stick and then have a passenger hold it in front of the car's speed-limit-recognition camera at all times...  

The whole business does sound frustrating.  It leaves one questioning whether such technology really does make the roads safer.