Engineer droids were B1 battle droids specially programmed to perform as battlefield technicians, pilots, and demolitions experts for the Separatist Droid Army. They were distinguished by the yellow markings on their head and shoulders, similar to that of the OOM command battle droids (sometimes they had the appearance of a B1 battle droid). Their programming allowed for the operation of virtually every vehicle-allied or otherwise in existence. They would usually engage their targets from close range.
Their advanced programming allowed them to easily adapt to the controls of most vehicles. They were also effective at repairing damaged vehicles as well as slicing into enemy vehicles for capture or sabotage. Their armament included a Shotgun, Detonation packs, and a F-187 fusioncutter. Because of the versatility of their arsenals they were valuable assets to the CIS on any battlefield.