Nissan Repair: 2002 Nissan Altima, crankshaft position sensor, 2002 nissan altima

Question
That is what the printout say's "Crankshaft Position Sensor A -Circuit Malfunction" Code-PO335.I didn't say anything about a camshaft error.Is that what the other sensor is-the camshaft ? Or are there 2 Crankshaft Position sensors ?
Thks
Dan

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-----Question-----
Have had intermittent problems with engine stalling @ low to idle speed.Other times it may stumble around 25 - 40 mph.The rest of the time runs fine.Also,"service Engine" light never coming on.Just this week stalled coming to a stop and "Service Engine" lite did come on.Had it ck'd @ Advanced Auto and got a Po335 code.That came up as "Crankshaft Position Sensor A Circuit Malfunction" error.The engine is a 4 cyl.Went to get the sensor and was told by Nissan there are 2 sensors and since it wasn't ck'd out by Nissans computer that may not be the problem @ this point not sure which to replace or just replace both?Now the svc engine lite is out and they say nothing will come up now but the engine was still occasionally stumbling.I have been power braking it coming to stops to keep the engine from stalling.What do you think ?

-----Answer-----
Dan,

I would go back to the parts store and get them to read the code again.  It should still be in memory even though the lite is not on.  It is probably the crank position sensor and not the cam position sensor from the code you gave.  Email me back with what you find.

Answer
Dan,

The one in the cover is the cam position sensor and it fires the injectors.  The one that is on the back of the engine works off the flywheel and it fires the plugs.  Basic square wave generator.  A magnet passes a sensor and lets the computer know to fire the plugs.  The sensor goes out or the magnet is defective and things go south...