The pair were found unconscious in a home in West Jordan where they had parked their van in an attached garage with the motor running.
The victims were taken to Jordan Valley Hospital where they both died Saturday night, Fire Chief Marc McElrath said.
Police were interviewing neighbors to find additional details about the incident. Officers were not able to immediately enter the home due to a buildup of the gas, the Salt Lake Tribune reported.
McElrath said it was not known if anyone was living in the house or if it was vacant and being cleaned before being put up for sale.