Neil John Lewis, 47, from Cardiff, pleaded guilty to one count of fraud by false representation and was sentenced at Cardiff Magistrates' Court.
The court heard that Lewis owned G and J Motors for 21 years and voluntarily surrendered his testing certificate following the incident.
Eve Smith, 21, Darcy Ross, 21, and Rafel Jeanne, 24, died when the car crashed into woodland in St Mellons, Cardiff, in March 2023. They lay undiscovered for two days. Two other people in the vehicle survived.
The fraudulent MOT was issued just weeks before the crash. Lewis had previously entered his guilty plea to the fraud charge.