Where is the fuel pressure sensor on a 2003 sentra 1.8

P1273 Nissan P1273 Nissan - Air Fuel Ratio Sensor 1 Lean Shift Monitoring Bank 1 Possible causes
- Faulty Air fuel ratio (A/F) sensor 1 Bank 1
- Faulty Air fuel ratio (A/F) sensor 1 heater Bank 1
- Fuel pressure
- Faulty Fuel injector
- Intake air leaks
- Faulty Air Flow Meter
Most probable is you have a bad heater in your upper bank 1 O2 sensor. Replace all of your O2 sensors.

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First pull the fuel filter and check that. There is a video that shows how to check pressure at the firewall.
https://www.youtube.com/watch?v=l8qweNkBp5All.

code po105 refers to manifold absolute pressure(MAP)sensor/barometric pressure (BHARO) sensor -circuit malfunction==causes--wiring MAP sensor--BARO sensor--ECM
code p0171 refers to system to lean bank 1===causes intake/exhaust leak---AIR system MAF/MAP sensor fuel pressure /pump /injectors--HO2SW
code p0325 refers to knock sensor(KS) 1 bank 1-circuit malfunction====causes--wiring ---poor connections---KS
Check the exhaust flexible pipe at the manifold for cracks
have a fuel pressure test done on the fuel manifold to determine either pump/ filter or pressure regulator.
replace HO2S unit

CODE PO171 FUEL TRIM BANK 1 MIXTURE TOO LEAN. POSSIBLES CAUSES, INTAKE AIR LEAKS, AIR FLOW SENSOR 1, CLOGGED FUEL INJECTOR, EXHAUST GAS LEAKS,INCORRECT FUEL PRESSURE CLOGGED FUEL FILTER, LACK OF FUEL FAULTY FUEL PUMP,FAULTY MASS AIR FLOW SENSOR,INCORRECT PCV HOSE CONNECTION.

It could be a number of things. Have you tried to run any codes yet?

Could be TPS, could be clogged cat converter, could be fouled/worn spark plugs, could be not enough fuel pressure, could be timing, could be......

no their mistakes could not have led to the issue. just their bad diagnostics missed it to begin with. the dealers do not always have the most competent shop. i would usually tell people to stay away from them and use the other shops around. you are not the first that i have heard with problems they cannot diagnose. go get a second opinion from another certified shop.

damaged fuel pump sending unit change it! but check power to fuel pump first

The MAF will not cause a miss on just one cylinder, here are the things that will, low cylinder compression, defective fuel injector, intake manifold vacuum leak at the gasket, and of course ignition system problems.

if it cranks for a longer time than normal and than it starts, you my friend need a new fuel pump rebuild kit/pressure regulator inside the gas tank. what happens is that the fuel will go back into the gas tank instead of staying in the fuel line and everytime you turn the key, the pump has to pump fuel all the way to the injectors again to get the car started. So, long crank and than start means fuel pump rebuild kit/pressure regulator in tank.