I had just driven through the square, when another car came round a corner too fast, skidded, and went out of control.

out 在这里表示"脱离、失去"的状态。 of 表示所属关系，连接"控制"和"失控"的状态。 control 的意思是"控制、掌控"。 out of control 是一个固定短语，字面意思是"脱离控制"，即"失控"的状态。