Maybe the answer to your question in this
post is that the tyre sensor valve seal has allowed moisture into the tyre. When it's cold the moisture freezes and doesn't effect the signal but once wet you got problems.
Alternatively I am guessing !
Here some info from Renault Fault Finding Guide
Make sure that the coloured rings are in their original locations (see diagram on the driver's side door).
Make sure that the pressure measured by pressure gauge is in conformance with that shown on the driver's side door, in the driver***8217;s handbook or in Workshop Repair Manual 364 Section 35 A for the type of wheels
fitted on the vehicle.
If the tyres are warm, add 300 mbar to the recommended pressure.
If the pressure is readjusted, perform a road test for at least one minute at a speed greater than 20 kph to force the wheel sensors to transmit.
Read the pressure values in parameters PR003 to PR006. If the difference between the pressure gauge measurement and the reading on the diagnostic tool shows scatter (uniform difference on the four wheels >300 mbar), readjust the pressures taking into account the pressure gauge scatter.
Wait for one minute for a further wheel sensor transmission.
Ok so maybe that's no help but please try the over infaltion method..
There's more info...
***8211; The sensors are activated about one minute after the vehicle has been running at a speed exceeding 20 kph.
***8211; When driving, the sensors emit signals every minute.
***8211; The sensors remain activated for 15 minutes after the vehicle stops, then go into standby mode.
***8211; In standby mode, the sensors emit signals only if they detect a pressure difference between two successive
measurements exceeding 68 mbar or if the pressure difference since last emitting exceeds 68 mbar (due to tyre
***8211; The tyres are considered to be cold when the vehicle speed has been zero for 1h 45 min.
***8211; The minimum time for detection of a leak is approximately 15 minutes.
***8211; The message "Pressure unsuitable for the speed" is activated only if the vehicle travels at more than 170 kph
(as an indication) for 3 minutes and the pressure on at least one of the tyres is 400 mbar less than the
recommended pressure at low speed. This message is inactive if the tyres are inflated to motorway pressure,
irrespective of the vehicle speed.
***8211; Alert thresholds:
***8211; over-inflation when cold = recommended pressure + 700 mbar
***8211; over-inflation when warm = recommended pressure + 850 mbar
***8211; under-inflation = recommended pressure - 400 mbar
***8211; major under-inflation = recommended pressure - 600 mbar
***8211; imbalance = pressure difference between the LH and RH wheels on the same axle exceeding 500 mbar
***8211; Informative messages displayed for the driver:
***8211; "Puncture: Change tyre" + STOP warning light + the wheel concerned fills up on the instrument panel
***8211; "Readjust tyre pressure" + the wheel concerned fills up on the instrument panel display.
***8211; "Inflate tyres to motorway pressure" + the wheel concerned fills up on the instrument panel display.
***8211; "Tyre sensor inoperative" + the wheel concerned is erased.
***8211; "ELECTRONIC FAULT" + "Service" warning light + the wheels concerned disappear from the instrument
To know whether the message displayed on the instrument panel is indeed due to a request by the SSPP system,
refer to Workshop Repair Manual 366 Section 83A, Instrument panel.
***8211; No display of the tyre inflation pressure on the instrument panel on MEGANE II.
Assuming all that does not solve the problem you''ll need to take your megane to a renault dealer or good indep renault garage. They should be able to tell you if one of the sensors is faulty - replace it - and reset the system..