Your employer should not come running to you for the reimbursement of repair costs which the dealer claims are not covered under warranty. Where the dealer has provided the car with a warranty against defects the dealer must comply with the terms of this warranty.
Even if the defect is not claimable under the warranty, there are further protections under the Australian Consumer Law that apply to new and used vehicles sold to a consumer. This includes a guarantee that the car be fit for purpose and of an acceptable quality. Where your car has broken down this usually amounts to a minor failure which the dealer must fix within a reasonable time. Unless it can be shown that you used the vehicle in an abnormal way or were aware of the defect prior to using the car, the repairs necessary to fix the car will be covered under this guarantee between the dealer and your boss. You will also be able to claim through the dealer any additional costs you incurred in finding alternative transport while the vehicle was inoperative.