Where is the o2 sensor in this car

The 1st sensor is located closest to the engine and the last is located at the rear of the exhaust system. Generally, if we are talking about O2 sensors: Sensor 1 = Before Catalytic converter Front (Upstream O2 sensor) Sensor 2 = After Catalytic Converter Rear (Downstream O2 sensor)
https://mechanicbase.com/troubleshooting/bank1-vs-bank2/

o2 sensors are at the rear of the cat converter-- HO2s sensors are at the front of the cat converter . Use the special tool to remove /replace them as if you don't then the wires will be damaged.

The front sensor should be in front of the catalytic converter.

Hi there:
There is a sensor located before a emission device called a catalytic converter that is located on both sides. The sensors in the back of the engine are called O2 sensor 1 bank one, (sensor before the catalytic converter) and O2 sensor 2 bank one (located after the converter).

On the front of the engine, going down you have two as well for there is a converter on both sides. first one coming from the engine is O2 sensor 1 bank 2 and then your failed one after the converter, O2 sensor 2 bank 2.

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Possible O2 sensors:

P2270 O2 Sensor Signal Stuck Lean Bank 1 Sensor 2
P2271 O2 Sensor Signal Stuck Rich Bank 1 Sensor 2
P2272 O2 Sensor Signal Stuck Lean Bank 2 Sensor 2
P2273 O2 Sensor Signal Stuck Rich Bank 2 Sensor 2
P2274 O2 Sensor Signal Stuck Lean Bank 1 Sensor 3
P2275 O2 Sensor Signal Stuck Rich Bank 1 Sensor 3
P2276 O2 Sensor Signal Stuck Lean Bank 2 Sensor 3
P2277 O2 Sensor Signal Stuck Rich Bank 2 Sensor 3
P2278 O2 Sensor Signals Swapped Bank 1 Sensor 3 / Bank 2 Sensor 3
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This is Bank 1 (closer to the dash panel) Sensor 2 (located after the catalytic converter).

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Note: A malfunctioning front oxygen sensor may cause fuel trim codes to set.

1. Several Diagnostic Trouble Codes use specific terminology to refer to sensor location. The illustration and key below explain the following terms:
2. Engine BANK Bank 1 is closer to the dash panel, (also referred to as RH or right hand). Bank 2 is closer to the radiator, (also referred to as LH or left hand).
3. UP Refers to Sensor 1 or "front sensor". It is located closer to the exhaust manifold and before the catalytic converter.
4. DOWN Refers to Sensor 2 or "rear sensor." It is located after the catalytic converter.
5. The following examples show how to interpret oxygen sensor terminology:
6. B1/S1 = Bank 1/Sensor 1 = Dash panel side, BEFORE the catalyst or "upstream"
7. B2/S2 = Bank 2/Sensor 2 = Radiator side, AFTER the catalyst or "downstream"

On almost every car, there is an O2 sensor located in the front, on the exhaust pipe, or manifold, and there is an O2 sensor located after the Catalytic converter. The front O2 sensor is the most important because it monitors the air/fuel ratio. The rear O2 sensor checks your Cat converter for proper operation and filtering.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

I believe they may be referring to the O2 Sensor, or Oxygen sensor. Being this is a 98, there may be two. If so, the first will be located on the exhaust manifold, the second, just before the catalytic converter. If there is only one equipped it will be located just before the catalyitic converter.

If you are not familiar with this part, it is the first "muffler" type part that is located just after the exhaust manifold and usually lies just under the passenger side of the car toward the front. You may need to raise the front of the vehicle to see it, as this is a small car and sits fairly low to the ground.

Typically, you will need a special socket called and O2 Socket to remove this and insert the new one, however if this is not affordable to you, then you can use an open end wrench. Be sure to disconnect the wiring harness first, then remove; and vise versa for inserting the new one.

Please let me know if you need further assistance with this matter.

carsandcomps,

Guru, Premium Expert @ Fixya.com

there are probably 4 o2 sensors, one below each manifold and 2 behind the catalyitic convertors

P0155 is o2 sensor heater circuit malfunction bank 2 sensor 1 it is the o2 sensor circuit in front of the cat converter the o2 sensors are located mounted to the exhaust pipe in front and behind the catylic converter the problem is in the circuit [wiring or sensor itself] check wiring and repair if necessary if the short or open circuit is the sensor need to replace sensor +++ P0161 is 02 sensor heater circuit malfunction BANK 2 SENSOR 2 ++++++ this is the sensor behind the cat converter

Oxygen sensors are always numbered like this:

Bank 1 sensor 1
Bank 2 sensor 1
Bank 1 sensor 2
Bank 2 sensor 2

some manufacturers use a kind of shorthand that reads different, but means the same thing:
Sensor 1/1 or O2s 1/1
Sensor 2/1 or O2s 2/1
Sensor 1/2 or O2s 1/2
Sensor 2/2 or O2s 2/2

Bank 1 is always the side of the engine where cylinder number 1 is located and, of coarse, Bank 2 is the opposite side.
On a 4 cylinder engine, there is only 1 bank and it is always referred to as Bank 1.

Sensor 1 is always the upstream sensor (The one located BEFORE the catalytic converter)
Sensor 2 is always the downstream sensor (the one that is located AFTER the catalytic converter.

Most GM engines have #1 cylinder located on the left bank, (or Driver's Side) of the engine,

So, the answer to your question would be that you are looking for the sensor located before the catalytic converter on the right (or Passenger Side) of the truck.