Ok, if the vehicle was sold "as is" without any type of written warranty, then you may have trouble forcing the dealer to make any repairs. When a vehicle is sold "as is" it is up to the potential buyer to have the vehicle thoroughly inspected to ensure it doesn't have any problems and is mechanically sound.
Nevada does have "lemon laws" but these typically only apply to new and used vehicles under warranty and can force the manufacturer to repurchase the vehicle if they can't fix a problem after repeated attempts. Unfortunately, NV lemon laws do not apply to used vehicles that are out of the factory warranty.
This is the specific law in NV:
Repairs to Conform to Express Warranties
.NRS 597.600 Definitions.
As used in NRS 597.600
, inclusive, unless the context otherwise requires:
1. “Buyer” means:
(a) A person who purchases or contracts to purchase, other than for purposes of resale, a motor vehicle normally used for personal, family or household purposes.
(b) Any person to whom the motor vehicle is transferred during the time a manufacturer’s express warranty applicable to the motor vehicle is in effect.
(c) Any other person entitled by the terms of the warranty to enforce its obligations.
So if the vehicle is still under a factory warranty, you could force the manufacturer to pay for any repairs that are necessary.
With that said, if you can have a dealer inspect the car and find out when the check engine light was most recently reset, you could have a cause of action for fraud and misrepresentation against the seller even if the car is out of factory warranty. If they reset the fault code in an effort to conceal a problem instead of fixing it, then this can be considered fraud and would give you the right to sue the dealer for the cost of repairs if they won't voluntarily fix the car.