2004 Volvo S40 2.4I engine check light is on, light is cleared and returns a week later, engine drives normal with light on. codes read P0172 system too rich bank one, P0191 fuel rail pressure sensor circuit range/performance, P1090 fuel rail pressure sensor circuit. now i need to know how to test to see if its the sensor that is faulty or the wiring circuit, replacement of the sensor is over $1000 and cant be returned so need to know im making the right choice by changing the sensor. thanks

P0172 LEXUS - System Too Rich Bank 1
Possible causes
Faulty front heated oxygen sensor
Ignition misfiring
Faulty fuel injectors
Exhaust gas leaks
Incorrect fuel pressure
Faulty Mass Air Flow (MAF) sensor
https://www.autocodes.com/p0172_lexus.html

P0172 - System Too Rich (Bank 1)
The adaptive fuel strategy continuously monitors the fuel delivery hardware. The test fails when the adaptive fuel tables reach a lean calibrated limit. Refer to Section 1 , Powertrain Control Software, Fuel Trim for more information. Fuel System.

• Fuel Pressure Regulator (vacuum hose off, diaphragm leak, malfunctioning).
• Leaking fuel injectors.
• Fuel return line restricted.
• Fuel rail pressure sensor (incorrect reading).
• EVAP canister purge valve leak (when canister is full).

Base engine.

• Engine oil contamination.

Air Measurement System.

• MAF sensor (contaminated, damaged, or corroded connector).

View Freeze Frame Data to determine the operating conditions when the DTC was set. Observe the LONGFT1 and LONGFT2 PID(s). Refer to Section 2 , Adaptive Fuel DTCs Diagnostic Techniques for more information.

You need a repair shop to drive the vehicle with a professional
scan tool, for at least 25 miles

That way all the Emissions Monitors will run clear

If you fail to do that,your guaranteed to fail inspection

If any codes come back,then the vehicle has to be component
test & repaired

It sounds as though there was some pushing & poking, done by
I assume, a shop & parts changed,tested or in need of replacing,
who knows

You also will have freeze frame data at the time the codes are set,
to help with the diagnoses,IF-- you have a good shop to work on it,
so far that doesn't appear to be the case

I don't buy your hopeful rational --IF-- the oil has not been changed
(often)over the life of the motor,wrong oil used or the cam actuators
have failed,as is sort of where all this conversation has gone or
explained to you

If the cam timing is not correct,then yes, the oxygen sensor codes
may set- BUT- I don't buy the fact they go away & never come back

We could be here a long time,so I suggest you keep your line of
questions going at a repair shop. Their not wrong or far off,you just
need to understand how things work together in a motor or maybe
not play well with other parts under certain conditions

It could be an emmissions problem. Sometimes even the gas cap being loose can cause a code. Make sure to tighten the cap when done refuelling...you should hear repetitive clicks when its tight. Other components related to code p0172 are o2 sensor(bank 1) and catalytic converters. Hope this helps!

no not in the least
take the car to another mechanic asap they have disconected somthing and not re conected it
or they do not know how to reset the computer eithor way keep away from those morons

have you tried to goggle this?
Description of vehicle trouble code P0172. ... A code P0172 may mean that one or more of the following has happened: The MAF (Mass Air Flow) Sensor is dirty ...

U NEED TO TAKE IT TO A SHOP THAT HAS A VOVLO SPECIFIC SCAN TOOL.THE GENERIC SCAN TOOL HAVE TROUBLE READ THE VOLVO CODES ESPECIALLY IF U ARENOT DEALING WITH A TOP NOTCH TECHNICIAN

Go to a parts store and run a free diagnostic test. It will tell you the codes that have popped up and then you can fix it from there. That light means the computer is sensing a problem.

no such thing as a catalytic computer... there is a catalytic converter ... part of the exhaust system so they may now be "guessing" that it's an O2 sensor. take the car to autozone... they will scan the codes for free.... post the codes here tho the lads and lasses there are pretty clever and will probably tell you what the codes mean.

code p2404 is from a none volvo tester it would convert over to volvo code ecm 432a ,leak diag. pump failure,now dont play with it driving should be ok but you should take it to the dealer or a volvo only shop and read codes and fix it when your ready