Councillors voted unanimously on Tuesday to pursue legal action after the council’s technical advisers said BAM Nuttall should be held to account for further defects.
These include fixing problems including shallow foundations and inadequate drainage.
The decision reopens old wounds for the contractor on the ill-fated busway project.
BAM Nuttall has already paid the county council £33m in an out-of-court settlement last year to cover defects and extra work.
It is estimated the latest repairs could take three years to complete.
BAM was two years late in handing over the project and claimed the council owed them around £70m more than the £84m contract price, triggering a protracted legal dispute.
The contractor said the busway had cost it £152m to build and claimed it should receive an extra £43m on top of the £118m the authority had already paid them.
But in August 2013 after an on-going legal battle over the late delivery of the project, BAM agreed to pay back £33m bringing the price paid by the council back to the original contract value.
If the council succeeds in its latest claim the total project cost would rise to around £183m.
BAM Nuttall would not comment on the matter.