So the latest little test that the 405 has set me is to find out why the TPMS has stopped working. It always worked fine but recently there are no readings on the display. The screen comes up with recommended pressures but no readings from the wheels. No alarms or messages and iCarsoft doesn't show any faults. I've had the battery disconnected and just wondered if something needs to be reset.
Any ideas and thoughts welcome.
Pete

Take it for a spin

The tire learn and location process is ready to start when the vehicle has been stationary, or is travelling at less than 12.5 mph for 15 minutes. This is known as 'Parking mode'. The learn/locate process requires the vehicle to be driven at speeds of more than 12.5 mph for 15 minutes. If the vehicle speed reduces to below 12.5mph the learn process timer is suspended until the vehicle speed increases to more than 12.5 mph, after which time the timer is resumed. If the vehicle speed remains below 12.5 mph for more than 15 minutes, the timer is set to zero and process starts again 2018 SE SDV8 4.4 Byron Blue

I'm using the car regularly so I wonder why it would go into parking mode. It just seems strange that the light comes on and goes out just as it should and the display comes on with recommended pressures but actual pressures are all 0. I've been looking for a TPMS module but I don't think there is one, just a receiver. The old SOS limited function message is coming up every now and then and maybe that has something to do with it. New battery on it's way
The MOT is looming and I wonder if the TPMS not working is a fail, even though the light isn't on.

Check out the WS manual section 204-04
WHEELS AND TYRES there is lots of info there, including fault finding section, and image where the Tyre Pressure Monitoring System Control Module (TPMSCM) is located (over head console area) 2018 SE SDV8 4.4 Byron Blue

Thanks for the info Kot.
You may have pointed me in the right direction as I had the overhead console out a week or two ago to fit the 'Powerful UK' Tap in loom for dash cam. I had a look this afternoon add made sure that everything is tight and where it should be. I'll give it a run tomorrow and see what happens. If there's no change the next step will be to take the loom out and put everything back to normal before I start dropping the headlining to get to the receiver.
Thanks
Pete

AHA now you tell me
Its possibly the 433Hz signal is being compromised by your Camera's you installed see extract from WSmanual

Review potential electrical interference to the tire pressure monitoring system control module e.g. charging units, power adapters, laptop/Nav screens, etc

Check to see if after-market Front and/or Rear facing cameras have been fitted. If fitted, reposition them 2018 SE SDV8 4.4 Byron Blue

First job tomorrow is a shopping run But with the cameras off. I will return.

Well we got there in the end Kot,(almost) I removed the dashcam hard wiring and TPMS readings came back. Tried powering the camera from the cigarette lighter socket and they disappeared again. Disconnected it and they came back. It looks like the compromise might be TPMS or dashcam which is fair enough as long as I'm not causing any damage by blocking the TPMS signals or whatever. I hardwired the camera using the power adapter that came with it and the same adapter is used to power it from the cig lighter socket. Opinion on a dash cam forum is that it's the power adapter that causes the interference and they recommend powering it from a USB socket. I'll try that next and maybe a proper hardwire kit instead of my home made one.
Thanks for the help and I'll report back if I find a solution.

 2018 SE SDV8 4.4 Byron Blue

Well, after much testing and experimenting with a proper hardwire kit, a different camera from my other car and rear camera on and off. The conclusion was: Any camera and power supply = TPMS reading zero.
BUT yesterday it started working ...with front and rear cameras on????
I've got no idea why, yet another example of the car playing tricks on me.