Biggest waste ever. You would do more damage than good. If you used a dry chemical extinguisher, you can forget about ever getting that stuff off your vehicle. It'll get into electrical connectors, gauge movements, switches, your stereo, air vents, etc. Your car is as good as totalled.
Then there is the safety factor, you might as well as run, even if you're thinking about using the chemical extinguisher. Most fires start as electrical fires and if you think you're gonna be opening the hood to find it, you're as good as dead because once the gas ignites...
The only good extinguisher is a halon extinguisher but a 5-lb bottle will cost about $100 dollars!