<!-- from fixya rte -->What is a upstream sensor - 2006 Chevrolet Uplander

You have 2 of those and also 2 downstream. You have two banks of cylinders and each one has an upstream o2 sensor and it is located in the exhaust manifold for each bank. Your scan tool should say Bank 1 or Bank 2.

The downstream sensors are after the catalytic converter.

What are the symptoms of a bad upstream O2 sensor? Sensor 1 Sensor 1 is the upstream oxygen sensor. It is the sensor that measures the oxygen content in the exhaust, providing an input to the computer, which determines how to adjust the air/fuel ratio. Sensor 1 is the sensor closest to the engine. Sensor 2 is the downstream oxygen sensor.
Mar 10, 2021

Bank 1, Sensor 1? Upstream or Downstream? - Newparts.com

https://www.google.com/search?q=2015+Chevy+Impala+3.6+upstream+o2+sensor+location

The 2005 Jeep Grand Cherokee Laredo 3.7L typically has two oxygen (O2) sensors. One is located upstream (before the catalytic converter), often referred to as the pre-cat or upstream sensor, and the other is located downstream (after the catalytic converter), known as the post-cat or downstream sensor. In many cases, the upstream and downstream sensors are not the same and serve different purposes in monitoring and optimizing the air-fuel mixture and emissions.

Bank 1 sensor 1 is an upstream on driver side (Cylinder 123) sensor 2 is downstream Bank 2 is on Passenger side, ***** sensor 1 is always an upstream*****

The upstream on bank 2, which is the opposite of bank 1. Bank 1 is the side with the number 1 cylinder. Downstream oxygen sensors (after the cat converter) are always sensor 2, as in Bank 2, sensor 2.

Ravi, I also have the same issue and confused between upstream left and right location.


I have problem with bank 2 sensor 1 and want to purchase a part. There are two part numbers 234-9007 for upstream left and 234-9009 for right.

So not sure the one on radiator (bank 2 sensor 1) side is upstream left or upstream right.

If you already know can you please reply?

Ho Joanne:
On Grand Cherokee oxygen sensor locations for 4.0 and 4.7 engines, check this diagrams...







The Oxygen Sensors (O2S) are attached to, and protrude into the vehicle exhaust system. Depending on the emission package, the vehicle may use a total of either 2 or 4 sensors.

Federal Emissions Package (4.0L and 4.7L engines):
Two sensors are used: upstream (referred to as 1/1) and downstream (referred to as 1/2). With this emission package, the upstream sensor (1/1) is located just before the main catalytic convertor. The downstream sensor (1/2) is located just after the main catalytic convertor.


California Emissions Package (4.0L engine):
On this emissions package, 4 sensors are used: 2 upstream (referred to as 1/1 and 2/1) and 2 downstream (referred to as 1/2 and 2/2). With this emission package, the rear/upper upstream sensor (2/1) is located in the exhaust downpipe just before the rear mini-catalytic convertor. The front/upper upstream sensor (1/1) is located in the exhaust downpipe just before the front mini-catalytic convertor. The rear/lower downstream sensor (2/2) is located in the exhaust downpipe just after the rear mini-catalytic convertor, and before the main catalytic convertor. The front/lower downstream sensor (1/2) is located in the exhaust downpipe just after the front mini-catalytic convertor, and before the main catalytic convertor.


California Emissions Package (4.7L engine):
On this emissions package, 4 sensors are used: 2 upstream (referred to as 1/1 and 2/1) and 2 downstream (referred to as 1/2 and 2/2). With this emission package, the right upstream sensor (2/1) is located in the right exhaust downpipe just before the mini-catalytic convertor. The left upstream sensor (1/1) is located in the left exhaust downpipe just before the mini-catalytic convertor. The right downstream sensor (2/2) is located in the right exhaust downpipe just after the mini-catalytic convertor, and before the main catalytic convertor. The left downstream sensor (1/2) is located in the left exhaust downpipe just after the mini-catalytic convertor, and before the main catalytic convertor.

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The Oxygen Sensors (O2S) are attached to, and protrude into the vehicle exhaust system. Depending on the engine or emission package, the vehicle may use a total of either 2 or 4 sensors.
Federal Emission Packages : Two sensors are used: upstream (referred to as 1/1) and downstream (referred to as 1/2). With this emission package, the upstream sensor (1/1) is located just before the main catalytic convertor. The downstream sensor (1/2) is located just after the main catalytic convertor.
California Emission Packages: On this emissions package, 4 sensors are used: 2 upstream (referred to as 1/1 and 2/1) and 2 downstream (referred to as 1/2 and 2/2). With this emission package, the right upstream sensor (2/1) is located in the right exhaust downpipe just before the mini-catalytic convertor. The left upstream sensor (1/1) is located in the left exhaust downpipe just before the mini-catalytic convertor. The right downstream sensor (2/2) is located in the right exhaust downpipe just after the mini-catalytic convertor, and before the main catalytic convertor. The left downstream sensor (1/2) is located in the left exhaust downpipe just after the mini-catalytic convertor, and before the main catalytic convertor.

The heater sensor I think you are talking about it is the upstream oxygen sensor. Sometimes the code reader just says heater sensor upstream and doesn't tell you its actually the heated oxygen sensor.

1/1 is upstream sensor on the number 1 cylinder side, 1/2 is the downstream of the number 1 cylinder side, 2/1 is the upstream of the number 2 cylinder side, 2/2 is the downstream of the number 2 cylinder side. Hope this helps.

these engines have 1 upstream o2 sensor and 1 downstream o2 sensor..the 1 in the rear exhaust manifold is the upstream and the 1 after the converter is the downstream..make sure you replaced the right one