TRQ oxygen sensors are manufactured to precise specifications using premium raw materials to optimize your vehicle’s emission system. Each sensor is isostatically-pressed for improved strength and durability, and plasma-sprayed to improve sensitivity and prolong the service life of the sensors. Oxygen sensors wear out over time and should be replaced every 60,000 miles to prevent poor engine performance. TRQ recommends replacing the oxygen sensors in sets to optimize fuel economy and reduce overall emissions. All products are fit and road-tested in our Massachusetts R&D facility to ensure we deliver on our promise of Trusted Reliable Quality.
Product Features
Application Specific Design: No modifications and pre-calibrated
Isotatic-pressed and plasma-sprayed for extended service life
Double-Layered 310S Stainless Steel: Additional protection from moisture and debris
Restored Engine Performance: Improved fuel economy and lower emissions
What is Upstream vs. Downstream?
Upstream location is between the catalytic converter and the engine
Downstream location is between the catalytic converter and the tailpipe
Install Tip: You may be required to reset the vehicle computer after installation of this part.
Quality Tested - built to a strict level of product standards.
Item Condition:New
Attention California Customers:
WARNING: This product can expose you to chemicals including Lead and Lead Compounds, which are known to the State of California to cause cancer, and birth defects or other reproductive harm. For more information, go to www.P65Warnings.ca.gov.
Lifetime Warranty
This item is backed by our limited lifetime warranty. In the event that this item should fail due to manufacturing defects during intended use, we will replace the part free of charge. This warranty covers the cost of the part only.
Returns: Parts with electrical components cannot be returned once installed.
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Expedited is available on checkout to the United States, excluding Alaska, Hawaii and US Territories as well as P.O. Boxes and APO/FPO/DPO addresses. Final shipping costs are available at checkout.
O2 Sensors is it Upstream or Downstream
Created on:
Tools used
No Tools Needed
1. Identifying your Oxygen Sensors
Upstream oxygen sensors are located in between the engine and the catalytic converter
Downstream oxygen sensors are located in the catalytic converter or farther away from the engine than the catalytic converter
Locate your vehicle's firing order diagram
The bank that contains cylinder one is bank one
The bank that does not contain cylinder one is bank two, even if it does not contain cylinder two
Hi, I'm Mike from 1A Auto. We've been selling auto parts for over 30 years. We're dedicated to delivering quality auto parts, expert customer service, fast and free shipping, all backed by our 100% satisfaction guarantee. Visit us at 1AAuto.com, your trusted source for quality auto parts.
In this video I have a couple of oxygen sensors with me. While there are some aesthetic differences here, the wire lengths are a little different, the actual body and tip of the sensor are a little different, the threads and gasket are the same, and on the other end the connections are actually the same. I can plug these into either position on our vehicle. But if I had to ask you which one's upstream and which one's downstream, you probably can't tell just from looking at them. That's true of most oxygen sensors. The way you determine whether or not an O2 sensor is upstream or downstream is all done visually.
Your oxygen sensor position can be determined relative to your catalytic convertor. As the name suggests, upstream sensors will be located upstream or ahead of, in front of, above, closer to the engine than your catalytic convertors. This means that they see the exhaust gasses first. They then go through the catalytic convertor and to the downstream oxygen sensor, which will either be located in the catalytic convertor like our vehicle here, or after the catalytic convertor to monitor the gasses coming out of the cat and make sure that it's being efficient relative to the readings of the upstream O2 sensor.
The other determination you need to make is bank one versus bank two. Determining which bank is which can be done by looking at a picture of your vehicle's firing order. Whichever bank contains cylinder one is going to be bank one, and the other one, regardless of whether or not cylinder two is in it, is going to be bank two by default. These banks are true of V engines like V8s, V6s, and flat engines like Porsches and Subarus that have individual banks.
On inline four-cylinder engines, as long as they have one exhaust manifold like a Jeep four-liter or a four-cylinder Honda engine, you'll only have one bank with an upstream and downstream O2 sensor. There will be no bank two on the engine.
On our vehicle here, this is the passenger side, which we've already determined from the firing order is bank one. We have our upstream sensor here closest to the engine ahead of the cat. Then we have our downstream or sensor two here inside of the catalytic convertor. This could also be located somewhere after the cat. Here I have my two sensors for the vehicle. While they are aesthetically different, we can now tell this is my upstream sensor because it looks just like the upstream sensor I have up there. This is my downstream sensor. Now that we know which one's which, we can order the right part, correct the problem, and fix you up right.
Thanks for watching. Visit us at 1AAuto.com for quality auto parts, fast and free shipping, and the best customer service in the industry.
OSA61670
In Stock
Product Reviews
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4.53/ 5.015
15 reviews
5 Stars
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Ian
March 8, 2018
Parts are good, delivery was good on your side of the boarder. When it cross over to Canada hard to track. Stupid Canada Post.?? I will be ordering more parts from 1A auto. Cheersss Ian
Purchasing From 1A Auto
J
April 27, 2018
Great web site, help videos, part prices and selections. I have used this web site for years and will continue to make my purchases from 1A Auto.
Satisfied
Y
March 1, 2019
Best price and just what my mechanic needed to make my drive & gas mileage more desirable!
Excellent
S
March 14, 2019
Came on time works very well plug n play n very good price I recommend it I got it for my 02 bmw 330i sedan that has the 3.0 l I6
Z3 parts.
Danny
July 13, 2019
Parts were received fast and the fitment was spot on. Good place to do business with.
Service
Ted
August 20, 2019
The item arrived quickly and was installed without issue! Prices were reasonable, would purchase from 1AA again.
D
October 15, 2020
Perfect
Heinz
January 23, 2023
They work really good .
Thanks. Heinz
Oxygen sensors work just fine
Rick
May 26, 2023
They were a perfect fit just like the original ones I took off no more check engine light
Joseph
June 7, 2023
They worked and error codes are gone.
Don
July 23, 2023
One is not working properly
Perfect fit
Bryson
December 21, 2023
Came in packaged securely. No damage. Fit like a glove
TRQ 5stars
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Yonnatan
January 24, 2024
They were easy to install, fitt perfectly, and they look great
Just what i ordered!
Matthew
April 8, 2024
Really quick delivery ,great price .Fit car as stated, will order more parts in future.
Martin
November 10, 2024
Fits and with the video, it was easy to install.
Customer Q&A
Will work for a 2003 330i after 03/03 production? If not what will?
2003 BMW 330i L6 3.0L (Built Before 3/03 Production Date) Upstream O2 Oxygen Sensor PairApril 19, 2018
Lindsey C
this O2 fit on 2004 BMW X3 L6 3.0 automatic transmission?October 20, 2023
Jose L
10
I dont know about the X3 because I have a 325xi which used those for the pre-cat O2 replacement.
October 20, 2023
Davy J
10
These parts will only fit the manual transmission. Currently, we do not carry this part for your vehicle. We're always updating our inventory so please check back soon!
October 20, 2023
Meghan R
10
I dont know about the X3 because I have a 325xi which used those for the pre-cat O2 replacement.
October 24, 2023
Davy J
I cannot get drive cycle to work to pass smog on a 2002 X5 will this help to the drive cycle. ?February 18, 2024
Robert L
10
Maybe wrong gas grade, use premium
February 18, 2024
Joe J
10
I am using premium, the X5 runs great, Do you have another suggestion.
March 14, 2024
John D
Customer service
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