Brakeslast - Mercedes Benz GL500 5.7 Litre 2007 Model

Mercedes » GL-Class » 2007-2012

Warning light (yellow triangle with !) flashes and power cuts out.
At first it was at highway speed only but now at low speed also.
It happens when I come off the throttle. The motor seems to die, about 65% loss of power but comes back if I stay off the throttle for a second or 2. The flashing light stops but returns in identical fashion as above.