Digital trigger from a weak signal
That's a pretty healthy pulse, actually, but the automotive environment is noisy. Looks like it is ringing quite a bit, hard to tell with that slow a timebase, but I'm not sure a ST will help here. You may want to just trigger a one-shot with a comparator. 

Maybe something like a TLV3501, which is a fast-ish CMOS input comparator. Clamp the input voltage to ground with a pair of fast diodes (eg. 1N4148) and feed (through a resistor) to one input and ground the other input. The input should also go through a resistor to a bias voltage of about +100mV to keep the output in one state (and provide a path for the bias current of the comparator). 

That should give you a logic-level pulse train with defined idle state. You can then capacitively couple that to a one-shot (eg. 74HC123) to generate a clean 1usec pulse (or whatever, but much longer than the ~100nsec ringing we see in your trace).