Replaced crankshaft sensor and engine light comes on.

SOURCE: 2003 Nissan Altima 2.5S, Check Engine Light Problem.

this problem could be caused by the mass air flow censor, i had the same problem with my car. it is really pricey at the dealer so you might want to check elsewhere for this part. I found one at a scrap yard for 85% less that the dealer and i also got life time warranty, the dealer does not offer any warranty on this part.

SOURCE: 2005 dodge crankshaft sensor

buy a new car or try the camshaft position sensor

SOURCE: Crankshaft and camshaft position sensors

MAke sure you replaced the right sensor and it's the proper design.(If you bought a generic part, it;s probably the wrong thing) I replaced my cam and crank sensors with the generic ones from AutoZone and they had no effect. Took it to Nissan, they replaced both at my expense, AND REPROGRAMMED THE ECU. That fixed that problem SES light hasn;t come on in 6 months....Fingers crossed

SOURCE: 1997 Bonneville - Engine light code P0303

the code you have is for a misfire on #3 cylinder. (im sure you knew this right?). the crankshaft position sensor will not cause one individual cylinder to misfire. what i typicaly do in this scenario is switch the ignition wire off of the guilty cylinder onto a known good firing cylinder and see if misfire moves to the other cylinder. i repeat this process by switching the spark plug and finaly the fuel injector. a compression check may be in order as well (but not a likely cause) unless you have access to a tech 2 (gms diag computer) you will need to clear this code after each component is moved and see if you get a new code ie :p0304 if switched to #4 cylinder..other wise if you do have access to a computer that has a misfire chart in its features you can quickly identify the guilty component. as i side note the ignition coil may also be faulty, but i believe your vehicle has a 3.8liter meaning that it has a coil pack....switch the others i listed and see ow you make out....good luck!

SOURCE: CRANKSHAFT/CAMSHAFT SENSOR DEFECTIVE

Maybe oil or coolant leaking on it shorting it out! Good Luck!!!!