Engine sputters on iddle.

bank 1 on front wheel drive car is the side next to the radiator or front of the car,sensor 1 is the first sensor you see on that exhaust manifold

HO2S( heated sensor) are before the cat convertor either in the manifold or exhaust pipe to the cat converter
O2 sensors are in the exhaust after the cat converter/s
I am drawing the difference because they are not all O2 sensors as each has a different operation for the position in the exhaust
the missing one will be in the exhaust manifold or pipe at a convenient position for servicing before the cat converter

The bank one sensor one O2 is located in the exhaust pipe before the Catalytic Converter, bank one is the cylinder bank that also contains the number one engine cylinder, in your car that would be the cylinder bank at the rear closest to the firewall (see diagram below). You will need to raise the car and crawl under it to replace the sensor and you will need a special O2 sensor socket. Remember always use safety stands to support the car when under the car for any repairs.
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follow the exhaust under neath the car. its located just behind the transmission on the top side of exhaust pipe

Under hood, center, front engine area, above exhaust pipe flange, mounted in exhaust manifold
Application:
Front
Under hood, center, rear engine area, above exhaust pipe flange, mounted in exhaust manifold
Application:
Rear

The oxygen sensor may be difficult to remove when the engine temperature is below 120°F (48°C). Excessive force may damage the threads in the exhaust manifold of exhaust pipe.

1. Start the engine and let it warm up to 120°F (48°C), stop the engine and disconnect the negative battery cable.
2. Detach the electrical connector from the oxygen sensor.
3. Using a special, oxygen sensor socket, remove the oxygen sensor from the exhaust manifold or exhaust pipe.

NOTE A special anti-seize compound is used on the oxygen sensor threads. The compound consists of liquid graphite and glass beads. The graphite will burn away, but the glass beads will remain, making the sensor easier to remove. New or service sensors will already have the compound applied to the threads. If an oxygen sensor is removed from the engine and if for any reason, it is to be reinstalled, the threads must have this anti-seize compound applied before installation.

1. Coat the threads of the oxygen sensor with anti-seize compound 5613695 or equivalent.
2. Install the sensor and tighten it to 30 ft. lbs. (40 Nm).
3. Reattach the electrical connector to the sensor and the negative battery cable.

Fig. Location of the rear O2 sensor


Fig. Location of the the front O2 sensor


Fig. Use a wrench or special socket to loosen the O2 sensor


Fig. When replacing or reinstalling an oxygen sensor, be sure to lube the threads sufficiently

the o2 sensors are located on the manifold and exhaust pipes under the car

Standing in front of the car looking at the engine bank 1 is the cylinders on the front of the engine. These are cylinders 1-3-5. On the rear is bank 2 cylinders 2-4-6. The O2 sensor is located screwed into the exhaust manifold or the exhaust pipe on the front of the engine.

okay po442 isevap leak check gas cap amd right front tower in engine check evap line for broken hose,po131 bad o2 sensor top sensor on rear exhaust manifold,po420 is bad catalyic converter but could be o2 sensor.i would replace o2 first reset eng lingt and go from there, hope this helps good luck.

You need to check two things.

First, there is a heat shield on top of the front of the motor where the o2 sensor you already replaced is. It's got (4) 12mm bolts. Remove it and check the exhaust manifold (big thing you put the o2 sensor into) for cracks. If there are any cracks, you'll get o2 sensor codes. Replace the manifold.

Second, if the manifold is fine start the car and listen to the exhaust pipe under the engine for leaks. Or if you already know the exhaust is loud... that's gonna do it too. A leaking exhaust pipe on an Accent will set secondary o2 sensor codes.

SHOULD you try to change it yourself, you will need a 7/8" wrench, and a new o2 sensor, or flex pipe, or manifold depending on what's broke. Do NOT touch the tip of the new or old o2 sensor to ANYTHING when you take it out or install it or it will be ruined permanently. Run the car until it's at it's normal operating temperature. Raise the vehicle, and take the o2 sensor out of the car (see below to understand which one) using the 7/8" wrench or if you got fancy and bought an 02 sensor tool... use it.

Replace whatever parts are bad (manifold or pipe) or just replace the sensor you need. Then restart the car and take it to a parts store and have them clear the code. The code (and check engine light) won't return right away, it usually takes a few days. If you did everything right you should be good. If not, it's not a terribly expensive job to have done and by now you should be able to explain to them what's wrong based on what you found when you looked at the car. Just tell them everything you checked and what you saw.

Education: I'm not sure where that half baked answer about o2 sensor 1 being near cylinder one came from but here's the real deal.

Sensor 1 is always BEFORE the catalytic converter
Sensor 2 is always AFTER the catalytic converter

Bank 1 and Bank 2 refer to which SIDE of the exhaust on 6 and 8 cylinder engines. Bank 1 is usually left side, Bank 2 is usually right side.

So... O2 sensor B1S1 refers to the O2 sensor BEFORE the converter on the LEFT side of the motor.

I just got done replacing the O2 sensors in my 99 Cougar due to throwing a P0135 malfunction code. There's 3. Facing the engine there's one in the front coming off of the front header, which is easy to get to. Another more tricky one if between the engine and the fire wall on the rear header pipe. The third is under the vehicle behind the transmission pan on top of the exhaust. In order to replace the O2 sensor near the fire wall you will need to remove the 4 retaining bolts for the ECM module and move it out of the way. Additionally you will need to remove the 2 retaining nuts for a wiring harness that is seated below the ECM module. Pay close attention to the connectors because the front and under vehicle O2 sensors have round connectors the one near the firewall has a squared connector. I was able to replace all 3 by myself in approximately 35 minutes. If your throwing a O2 heater malfunction code it is most likely going to be the sensor near the firewall. make sure that you know someone with a code reader so the code can be cleared. If you're do for an emmissions inspection be sure to put at least 40 miles on the new O2 sensor with different types of driving (e.g. highway, coasting, decellerated turns and rapid acceleration). Gotta love project cars for your kids!!