If you have an "overheat" problem which comes from air temp measured upstream of the de-ice valves or "leak" problem which comes from pressure sensors placed downstream of the de-ice valves the CCAS is activated and AFR AIR BLEED FAULT LIGHT illuminates amber.
The other lights on DE-ICE panel will stay extinguished.
In order to determine what causes the problem we need to deselect AFR AIR BLEED pb. Now, if there was an overheat problem associated ENG pb would illuminate FAULT. If no light illuminates while AFR AIR BLEED is selected off, the reason is leak or low pressure.
Thats my understanding.