I have a 2001 nissan sentra xe and my check engine light is on i had a diagnostic test and the codes PO 455 and PO 0440 came back what does this mean?

po462 fuel level sensor,do you have two O2 sensors before catalytic con.Po420 will go off when you replace O2 sensors.

This link may be helpful.
Bob

https://www.google.com/url?sa=t&source=web&rct=j&ei=jVO4VK_hEMvbsAT83YDgCA&url=http://www.autopartswarehouse.com/shop_years/nissan-sentra-speed-sensor-2001.html&ved=0CDcQFjAA&usg=AFQjCNHmI3zYnmpPLAMrWGUYw4Hq3dw2tQ&sig2=NZHLkkBawd1OUJEZgAwLQQ

Visit your local auto parts store and they can pull the codes with their scanner and tell you what is needed.

check engine light on means some fault codes stored in your engine control module.
use this tool clear the fault code p1320.

check for spark/fuel/camshaft sensor/crankshaft sensor/coil pack/check engine with scantool for fault code

Some ECUs require a reset and this is often done via the diagnostic code scanner itself. Auto parts stores will scan free, but I don't know if they would charge to reset the error register. You would have to call them and ask.

The only way to tell why the light is on is to have an engine diagnostic test done which will pinpoint exact problem. Many part stores will do it for free. Most shops charge $40 which is well worth it. You can also go to autozone.com and register for full free online repair manual for your car.

Distributer Signal Output is code p1320........Intake Valve Timing Control Position Sensor Bank1 is code p1140...

There is a leak somewhere in the evaporative emission control system. The best way to test that is have a smoke test done on it to find out where the leak is. You'll have to call around to see if any repair shops have a smoke machine, or call a dealer.