Best one is an LS2000..they are DSO and user friendly..and altho they origianally were around $2 grand, you see them on ebay all the time for a couple hundred. Try and find one that also comes with the ign pick-up.
That scope will pick up anything on automotive systems.
Unfortunately, the days of diagnosing with a DMM and a test lamp are disappearing b/c of the technology and a DSO is now just commonplace in any shop. But the upside is now you can buy one for cheap..and once you own one , you will wonder how the hell you got by w/o it.
You can look at any sensor and diagnose it in 30 secs w/o that " WONDER if 'dis is gonna' work " feeling you get as you buy an expensive part ..so, it pays for itself.
I see many post here where the poster says his Mechanic does not have a scope...RUN...that puts him in the same boat you are in...Guessing.

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A Dalton