One appliance and crew from Maidenhead and one from High Wycombe attended, along with two officers.
The car, in a layby around 1km north of the Bisham roundabout, was well alight when they arrived.
The firefighters used:
- Two sets of breathing apparatus
- Two hose reel jets
- Two environmental packs
Thames Valley Fire Control Service received multiple calls to the incident.
The road was closed while they worked at the scene.
The incident was left in the hands of Thames Valley Police.