The Subaru Forester pulled a caravan the wrong way along the northbound carriageway of the motorway in south Oxfordshire, hitting a Ford Mondeo and a Ford Focus.
The crash killed the Subaru driver and passenger, both in their 80s, and the Mondeo driver, who has been named as 32-year-old Stuart Richards.
Thames Valley Police said the car had been involved in a “damage-only” collision five days before Monday afternoon's crash.
Update in relation to M40 fatal collision— Thames Valley Police (@ThamesVP) October 18, 2018
•The driver of the Ford Mondeo who died has been formally identified as Stuart Richards, aged 32, from Stockport.
•TVP has made a mandatory referral to the Independent Office for Police Conduct.
Full details https://t.co/TTWfJUEAI6 pic.twitter.com/CGS9GdWgs2
It added that it had referred itself to the police watchdog.
The force said: “Thames Valley Police has made a mandatory referral to the IOPC in relation to the fatal collision, due to previous police contact.
“On October 10 this year in High Wycombe, a report of a damage-only road traffic collision involving the Subaru Forester was made to the force.
“The IOPC will now make a decision as to whether they will carry out an investigation.”