I have a nissan silvia s13. There was recently an accident, and what happened was somebody crashed into the rear of the car. I'm now getting a exhaust smell in the car. Any ideas?

dont have one

This could be almost anything from loose trim to broken body parts, you should get the car checked by bodyshop to make sure that it is safe to drive

Hole in the brake line or leaking wheel cylinder.

Have you had a four wheel alignment done recently? Do you replace all the links in their entirety, or just the bushes? If just the bushes, try an aftermarket set of poly bushes?
what happened just before 70k? Did you have a crash? Did you damage the axle/housing (bent rear axle)?
please tell us how you solved this problem as it could help someone else in the future..thanks.

Which sensor?

speed sensor is fitted to the abs system. if the abs system is fine with no faults coming up then it is down to the dash. now the dash is the most sensitive part, if you hit the dash to hard it can make this happen. also can make the connection to the dash and wiring come apart. braking the circuit. taking the dash out and cleaning the pins that connect the dash to the wiring can sort this out. failing this the speedo its self may be damaged and need replacing. you can hit the dash in an accident and you would not even know you have hit it. your brain does not register the movment.

Front air bags are not designed to deploy in side impact, rear impact or rollover crashes.There are several reasons why your air bag may not have deployed during a crash. The first reason is that perhaps your crash is not the type of accident where air bag deployment would be helpful. For frontal air bags, this includes many, but not all, side impacts, rear impacts and rollovers. This category also includes minor accidents in which the driver and front passenger (if there was one) did not suffer any significant injuries requiring medical treatment. Many people do not realize there are a lot of side air bags that do not deploy during a rollover accident, even when the vehicle rolls onto its side. That is because those side air bags do not include an appropriate crash sensor that can detect rollover crashes.

BEST THING TO DO IS PRESSURE TEST THE RAD. THIS WILL PRODUCE THE LEAK YOU HAVE IF SMOKE IS COMING FROM ENGINE IF SMOKE IS COMING FROM TAIL PIPE. GO TO PARTS STORE BUY A HEAD TEST KIT VERY EASY TO DO. LETS MAKE SURE NO HEAD DAMAGE WAS DONE AT TIME OF ACCIDENT.

ABS is...Anti Braking System.
Your car Nissan Silvia S15, your engine name is SR20. They made from Japan model.
There is plenty of Japanese import shop. Got spare with parts.. Find your local..Talk to Japanese people. They love on Silvia. :-)

Or look at EBAY?

sounds great