Nissan Sentra 2001 gxe with code p0420

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

Have someone check the exhaust back pressure.

I had same problem on my 2001 sentra gxe, no crank but dash lights up. thought it was the immobilizer system. found a blown fuse in the panel under the dash drivers side. 10 amp fuse labeled engine control

your ECM/ computer may be shot. those model sentras had campaign, where the ECM box would be lined with foam to hold the computer tight, but the fumes from the glue that Nissan used to hold the foam down, would eat the computer internally and destroy it. Nissan had us pull those foams out and discard. if you still have the foams inthere, good chances are that the ECM is fried, causing issues. Question: did you use aftermarket air filter in the air box?? or Nissan filter?? Let me know. very important to use Nissan filter it this car.

https://www.obd-codes.com/p0450

Take a few minutes to make sure you dont have a blown fuse....Run through them with your test light...

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

check spark plugs

It has a belt. You should replace it soon.

Have the battery tested and the alternator tested, the other issue may have a code stored to help point in the right direction, at that many miles things are bound to wear out.