1996 Pontiac Sunfire, code reads too lean, bank 1

no year car but is 1996 or newer sure.
there's always a better way, better tools and better skills.
for sure.3.8Liters.
why not replace all front O2 sensors first.
the number of sensors on cars can very by , FED or CALIF
car rules.
the error means the 02 cell is reading full lean all the time.
stuck near 0vdc lean, and has many reasons.
1;Heater in it dead (super #1 cause of dead sensors)
2: 02 is bad.
3: engine is injecting too lean.
4: exhaust leaks near ANY o2 sensor causes LEAN (false)
learn that exhaust PUTTS are both positive and negative.
boom, vacuum, boom, repeats have hard proof.

420 is a red herring, as that can not work until all 02 sensors start working then 420 cat tests can run. and pass.

the engine both banks are failing. so what is the likely hoot
why both sides? my guess is low fuel pressure or if car has MAF sensors it is dirty,
no year told so now EFI can be guessed, by me or anyone.

check the spark plug and coil pack. swap 2&4 coil pack with 1&3.
to see if the fault moves.

otherwise its a bit of guessing game without the dealer read out.

lean mix can be injector, coil, spark plugs, o2 sensor, camshaft sensor/adjustor, low compression due to valves, head gasket or piston rings.

idly if it start drive it, if possible, and see what additional faults appear.

I assume this is a 4 cyl and you changed the O2 sensor bank one sensor one. The code meanss the sensor is not switching back and forth between rich and lean as fast as it should be.
Could be an exhaust leak, or other engine problem. Could also be a problem with the engine thermostat.

The code P0137 means that your downstream O2 sensor has low volts. A rich running engine makes the voltage go high, not low. If the upstream sensor is not reading a rich or lean condition, then you need to replace your downstream O2 sensor.

Given that most of the trouble codes are for the O2 sensor, I think I would change it. The multiple misfires could be because of improper fuel/air mixture caused by a bad sensor. Disconnect the negative(-) battery terminal then change the sensor. Disconnecting the negative(-) should reset the computer and allow the fuel/air mixture to return to default allowing the engine to start.
P0130 - O2 Sensor Circuit Malfunction (Bank 1 Sensor 1)
P0134 - O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)
P0135 - O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
P0141 - O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
P0300 - Random/Multiple Cylinder Misfire Detected

First off have the ODBII engine codes read out. It will probably tell you that one or more of the following has a code:
1. O2 sensor Bank 1
2. Mass air flow sensor problem
3. Throttle position sensor problem.
4. EGR Valve problem

The OBDII codes will tell you which one it is.
My bet is either 2 or 3 above but would have to read codes first.

Thanks for using FixYa.

Kelly

BANK 1 SENSOR 1 IS THE ONE IN THE EXHAUST MANIFOLD. BANK 2 SENSOR 2 IS BELOW THE CATALYTIC CONVERTER.

P0171 SHOULD GO AWAY WITH A GOOD O2 SENSOR BUT DO CHECK FOR VACUUM LEAKS TO BE SURE. 3.1/3.4L ENGINES HAVE A BAD DESIGN INTAKE MANIFOLD GASKET, THE LEAK OIL, COOLANT, AND AIR.

Hi..my name is Keith...and the oxygen sensor(s) sends a signal to your computer to control the richness or leanness....and bank 1 is the exhaust pipe comming out of the drivers side of the engine..so..you probably need to replace the O2 sensor(s) or you could have dirty fuel injectors..not letting enough fuel into the cyclinders..i hope this will help

Replace your bank 1 (that's the cylinder bank with cylinder #1 in it, usually passenger side but verify this before changing parts) primary oxygen sensor. This is the one before the catalytic converter. The primary determines your air/fuel mixture, and if it goes bad, the computer will revert to preprogrammed fueling maps, which are fuel-rich by design (to safeguard the engine). Change the O2 sensor on bank one, before the cat, and maybe check your spark plugs as well (running rich too long will foul them) - for the minimal cost, it's worth changing them too.

When they say "bank," they're referring to cylinder banks 1 or 2. Bank 1 is the passenger's side and has cylinders 1-4 on it. Bank 2 is the driver's side and has cylinders 5-8 on it.

P0171/0174 indicates that the long term fuel trims have reached a maximum (should be somewhere around 30-35%). Fuel trims are how much fuel the PCM adds or subtracts. 0171/0174 indicates that the engine is running lean, meaning that outside air is getting past the mass air sensor. The O2 sensors see this excess air and the PCM responds by cranking up fuel trims to add more fuel for that more air.

Possible solutions include:

• In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
• Inspect all vacuum and PCV hoses, replace if necessary
• Check for a dirty fuel filter and proper fuel pressure