1996 Oldsmobile LSS. Went to autozone and got code PO133. 'Fuel system running rich or lean- check other aacodes first.' and 'Oxygen sensor defective'; The guy said it probably isn't the oxygen sensor; as it's been stalling recently and making a weird noise when it's turned on.

how about a PO133 ,,,should be the first in system

Schematic
The Oxygen Sensor 1 (O2S-1) is an electrical source that responds to oxygen content in the exhaust manifold. When the sensor reaches approximately 316°C (600°F), it produces a voltage based on the difference in oxygen between the atmosphere and exhaust gas. The PCM sends a bias voltage (391-491 mV) on the signal line which is pulled up through high resistance. When the O2S-1 is cold, it produces no voltage and has extremely high internal resistance. The internal resistance of the sensor is much greater than the resistance of the bias pull-up resistor. However, when the sensor heats up, it produces voltage that overrides the bias voltage. This voltage is read by the PCM to determine a rich/lean O2S-1 signal used to adjust injector pulse width. Under normal conditions, low sensor voltage means high oxygen content/lean air-fuel mixture and vice versa. Normal sensor readings will fluctuate between 10 mV and 999 mV DTC P0133 sets when the O2S-1 signal rich to lean or lean to rich average response time is too slow.

DTC PARAMETERS
DTC P0133 will set if the average response time of the LEAN to RICH switches is greater than 125 ms or the average response time of the RICH to LEAN switches is greater than 156 ms for 100 seconds when:
^ Engine speed is between 1500 and 3200 RPM
^ Loop status is closed
^ Calculated air flow is greater than 7 gm/s
^ Commanded air/fuel ratio is 14.7 to 1
^ No cam, CKP, ECT, EGR, EVAP purge solenoid, fuel trim, IAT, MAP misfire, system voltage or TP sensor DTCs have been set.

DTC P0133 diagnostic runs continuously once the once the above conditions have been met.

DTC P0133 is a type B DTC.

DIAGNOSTIC AIDS
Possible causes of DTC P0133:
^ An intermittent connection or corrosion in the O2S-1 harness connector can set this DTC. Use Scan tool to monitor O2S-1 voltage with engine running at normal operating temperature while wiggling the signal and ground wire. Make sure the sensor is tight.
^ The most probable cause for DTC P0133 is contamination. Check for obvious contamination (oil, fuel or engine coolant) by removing sensor. Identify and correct the cause of the contamination if contaminated. Replace the O2S-1.
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DTC P0133Circuit Description


After achieving closed loop fuel control, a commanded air fuel ratio of 14.7:1, RPM between 1,500-3,200, and air flow between 7-25 grams per second, the PCM will continuously monitor the front oxygen sensor signal for 100 seconds. During this time, the PCM counts the number of rich to lean and lean to rich switches. To be considered a switch, the voltage must go below 300 mv and above 600 mv. The PCM also keeps track of the time it takes to make the switch. The number of switches along with the time to achieve these switches are used to calculate the average response time to perform each switch. Also this information is used to calculate if the proper ratio of the switches is correct. The 3 diagnostic trouble codes listed below are used to identify different types of faults that can occur with oxygen sensors.

Conditions for Setting the DTC

DTC P0133
This DTC is set if the average response time of the switches from the sensor is too slow after the 100 second test is performed. If the lean to rich time is greater than 125 ms or the rich to lean time is greater than 156 ms, this code will set.

Diagnostic Aids
Repair Procedure
The oxygen sensor wiring and connections should be checked if any of these DTCs are set because corrosion or loose connections could cause these DTCs to set.
The most likely cause of setting any of these DTCs is contamination. This contamination could be caused by fuel, improper use of RTV sealant, engine oil, or coolant contamination.
The source of contamination should be identified and corrected before replacing the sensor.

You may have poor plug wires, or even a low compression cylinder. Also, make sure the air filter is clean. Your oxygen sensor (upstream) the one closest to the engine has detected a rich condition.

Is refer at O2 sensor, Code 51 - Oxygen sensor output indicates lean too long

Power loss light: Off
Limp-in mode: Engine allowed to run rich, but prevented from running lean

Possible Causes
Bad oxygen sensor - Replace the sensor which is located on the turbo housing near the down pipe (for turbo) or on the down pipe near the exhaust manifold.

Bad connection or wiring - Check the wiring and connections between the sensor and the logic module (or SMEC). Clean and regrease any corroded connectors with dielectric grease and repair any shorts. Look for melted wire insulation near the exhaust manifold. A shorted connection to ground or any positive source will cause this fault code.

Low fuel rail pressure - See the Diagnosing Your Fuel System page.

Diagnostic Method - Trigger Parameters
- In closed-loop
- Sensor output indicates lean for more than 715 seconds (11 minutes, 55 seconds)

Results If Component Fails
A fault code 51 is stored, the circuit stays in closed-loop, and the logic module will still monitor the oxygen sensor signal. If the condition persists for four times what it took to set the code, the logic module will allow the engine to run rich, but prevent it from running lean.

Hope helps.

Fault Code 51 - Oxygen sensor output indicates lean too long

Power loss light: Off
Limp-in mode: Engine allowed to run rich, but prevented from running lean

Possible Causes
Bad oxygen sensor - Replace the sensor which is located on the turbo housing near the down pipe (for turbo) or on the down pipe near the exhaust manifold.

Bad connection or wiring - Check the wiring and connections between the sensor and the logic module (or SMEC). Clean and regrease any corroded connectors with dielectric grease and repair any shorts. Look for melted wire insulation near the exhaust manifold. A shorted connection to ground or any positive source will cause this fault code.

Low fuel rail pressure - See the Diagnosing Your Fuel System page.

Diagnostic Method - Trigger Parameters
- In closed-loop
- Sensor output indicates lean for more than 715 seconds (11 minutes, 55 seconds)

Results If Component Fails
A fault code 51 is stored, the circuit stays in closed-loop, and the logic module will still monitor the oxygen sensor signal. If the condition persists for four times what it took to set the code, the logic module will allow the engine to run rich, but prevent it from running lean.

Hope helps.

P0171 indicates a lean condition. The most common cause of this is a defective mass air flow sensor. Also check if any vacuum leaks.Replace MAf sensor,if cleaning the MAF does not help.
OBD II P0172 Fuel System Too Rich (Bank 1).P0172 - System Too Rich (Bank 1) Essentially this DTC means that an oxygen sensor in bank 1 detected a rich condition.
When the code says that the Fuel System is "too rich," it means that the computer has been subtracting more and more fuel, which is called Long Term Fuel Trim. Ideally, the Long Term Fuel Trim should be close to 1 to 2 percent. When a code P0172 is set, it means that the Fuel Trim is anywhere from -15 percent to as low as -30 percent compensated. When this happens, the computer knows that there is an improper condition in the control of the Fuel System.


Thanks.

P0174 is SYSTEM LEAN BANK 2. If you do not have any rough running or missfires. Check for any vacumm hoses that may be damaged or loose. Any code that is set on OBDII has to be cleared with code reader. If you have any rough running or mussfires, check fuel injectors for proper operation. If this helps, please rate.

That is an oxygen sensor, these sensors send a signal to the computor to adjust the rich/lean fuel mixture.
When a code comes up for them, they generally need replacing.

The sensor is about the same as 1 hour labor time at the dealer, the sensor will not in most cases be defective with this code, something else is causing this engine to run rich.

ok so you have an oxygen sensor that went bad from the P0175 code and a random misfire code from the P0300. If it is random you might want to check your spark plug wires or spark plugs themselves and see if anyof them went bad. So get an oxygen sensor and replace it. This can also cause the second problem for it tells the computer that it is reading too rich. Well in this case all that unburnt fuel from the spark plugs or wires not igniting properly you will have a reading like that.
The most common issues for lean codes are:

1. Vacuum leaks - check for failed or loose vacuum lines, leaking intake gaskets, intake air tubes
loose or any other source of un-metered air leaks (leaks after the Mass Air Flow Sensor)
2. Restricted fuel filter or bent/pinched fuel system lines
3. Incorrect input from other sensors, such as the Mass Air Flow Sensor, which may not always drop a separate code
4. Engine misfire – Yes I know this one may seem weird. You might think that if there is a misfire then you will have all that unburned fuel and it should read rich; right? Well the O2 sensors read only oxygen content in the exhaust, so if you have all that unburned fuel from incomplete combustion then, you guessed it, you also have all that unburned oxygen. High O2 content in exhaust equals a lean reading!

fuel pressure regulator on the fuel rail is probably it or the egr valve is stuck open allowing burnt fuel to flood the intake, im leaning towards the fuel pressure regulator because the o2sensor is probably reading rich or if its reading lean then i would choose the egr valve . good luck