Drive slow 1/3 warning light

For starters, do you have an Owner's Manual?

Next, SLOW DOWN 1-4, no?

If so, the lights indicate an over-temp condition for the catalytic converters.

Could be a wiring problem, clogged converter or another issue.
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Since it happened at start-up it is probably an ECU failure. They hate moisture and you are in London. Open the trunk, turn the two quarter turn screws and fold down the carpeted firewall panel. The Cat ECUs are silicone faced boxes about the size of a deck of cards. If they are black faced they are original. Green face is the newer style. Disconnect them both, restart car. If no light then shutdown and swap boxes and see if light moves to other side. Then take out verified bad box and put on a warm dry place to drive out the moisture.Then reseal with silicone and hope for the best. Those little devils aren't cheap.

Dave

Edit, If you don't have Catalytic Converters disregard. I don't know what the light means in a Catless Euro Model.

 

In my 348 the SDL lights come on when I have the cat's temperature sensor disconnected
Maybe one is broken
Frank

 

Probably just need to drive. The electronics have a way if fixing themselves. You can try cycling the suspension switch to wake it up. Glad to hear you are enjoying the car.

Dave