ESP light will come on for all sorts of engine faults on these and Lexus, haven't got a clue why, had a LS220 just the other week with a DPF fault, (well known, and there are modified parts for them) and the ESP light was on!

Thinking about it I suppose if there is a control fault on the engine then the ESP could be disabled due to the ECU not being able to control engine out put accurately enough and the light is just to tell the driver that the ESP is off.