The ECU Job:
The Contract can be selected if it is one of the three available contracts on the GTA Online Protagonist’s Job Board in their Auto Shop.

Sessanta will tell the player that KDJ wants an ECU from an armored train so he can give it better uses. The player will need to learn which one of the container on the train will be holding the ECUs, and learn when they are due to be transported to be able to find a way to stop the train in order to rob it.

The Contract, like other Contracts, consists of two Free Mode preparation missions and one finale.

Prep Part 1:
Train Inventory –
“Identify which of the train’s containers will be holding the ECUs.”