Supppose you bought a second-hand car, having been told by the dealer that it was in excellent working condition. You drive it away and a mile down the road the engine warning light comes on. Think you can insist that the dealer repairs it? No, you can't. What you can do is obtain independent quotes for the work and submit them to the dealer with a, say, seven day deadline to inspect the vehicle and to produce his own quote. After the deadlnie has passed you could proceed with the repairs and then try to claim the money back from the dealer.
If you had paid by credit card you could apply to themfor compensation, but if the cost of the repairs is too much they may declare the car a write off. Best thing is to be very careful about buying a used car, especially at the cheaper end of the market, and use what you consider to be a reputable dealer.