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The deltaV needed to get from Mars to the sun would require fuel several orders of magnitude more than is curently being used, and several orders of magnitude more mass than the car.*
Have the car orbit Mars for a few hundred years, to then become a monument to man's endeavours / folly.
Or spunk thousands of tonnes of fuel into space (kinda littering it a bit) to drop it into the Sun.
* and no, I've not done the maths
Send up a one ton something with control and propulsion so that if it goes to plan it can be directed to the sun or something, not hanging around for eternity*.