There are around 15 minutes of delays with congestion back to Junction 10 for Wokingham after the fire at around 7am between Junction 7 for Slough West and Junction 6 for Slough/Windsor.
The Highways Agency anticipate normal traffic conditions by 9am.
Firefighters from the Slough station were called to the car fire which was out on arrival.
They had to briefly close the motorway while they moved the stricken car from the outside lane to the hard shoulder.
No-one was injured.