EY’s appointment follows a contracts review undertaken by KPMG that uncovered all the problems that led to the departure of chief executive Richard Howson last week and a 70% collapse in company value.
EY has been brought in with a specific focus on cost reduction and cash collection.
Carillion announced last week that it was undertaking a comprehensive review of the business and capital structure, in an urgent quest to reduce borrowings and meet debt targets.
Interim chief executive Keith Cochrane said: "We are moving forward quickly with the actions outlined last week. Alongside our own efforts, EY will provide support across the business and bring an external perspective to our cost reduction and cash collection challenge. My priorities are to reduce the group's net debt and create a balance sheet that will support Carillion going forward.
"We need to simplify the business and demonstrate that value can again be created for shareholders by focusing the group on its core markets, including infrastructure and property services, in which it has good strengths and leading positions."