Trying to locate upstream 02 sensor 2004 CTS 3.6L

There should be just 2 02 sensors on your car an upstream and a downstream

Here is the link for both the upstream and downstream 02 sensor

Amazon com B072WPRVF6

Do you have the 6-cyl or the 8-cylinder model? The P0135 code is for an upstream O2 sensor. The 6 cylinder has one up near the exhaust manifold and another (downstream) sensor just after the catalytic converter. The 8-cylinder has two upstream sensors, one on either side of the engine near the manifolds, and one by the catalyst. Be sure you located and replaced the correct upstream sensor. If that is not the problem, the issue could be the wiring harness going to the sensor. They run very close to the manifolds and often get damaged. Inspect the wiring leading back from the sensor to the PCM for melted and exposed wiring. IF you find some, you may be able to patch it, but often you must cut out the bad and replace the section with a new connector end. The sensor signal is relatively low voltage and doesn't handle damage wiring well.

Hi Jesus, Im AL the owner of Big As Auto Repair.

If you have a 4 cylinder engine then you will only have two 02 sensors 1/1 is upstream and 1/2 is downstream. Upstream is the one closet to the engine and downstream is the one farther away from the engine.

If you have a six OR eight cylinder engine you will have four 02 Sensors. 1/1 means Bank One Sensor One. 1/1 and Bank one means right bank and right bank means the side with the number 1 spark plug. SO, 1/1 means, "Right Bank" Upstream 02 sensor. 1/2 means, "Right Bank" Downstream 02 sensor.

2/1 means, "Left Bank" Upstream 02 sensor and 2/2 means, "Left Bank" Downstream 02 sensor. Hope this helps and please visit my auto-repair-website at: http://www.bigasautorepair.com/

HO2s ( heated sensors) sensors are fitted prior to the cat converter. O2 sensors are fitted after the converter.

cars have 2 to 4 sensors in the exhaust system.If it is throwing an 02 sensor could does not mean you have a bad sensor,it means at that sensor it is burning lean or rich.Example if code reads bank 1 sensor 1 fault that is the sensor closest to engine.

YOUR 02 SENSOR UPSTREAM IS LOCATED ....IF YOU LOOK RIGHT BETWEEN THE VALVE COVER AND RADIATOR YOU WILL SEE A EXHAUST SHIELD THE HOLE IN THE MIDDLE WITH THE SENSOR COMING OUT WOULD BE YOUR UPSTREAM 02 GOOD LUCK

Heated Oxygen Sensor The sensors are located in the exhaust system. On some vehicles, one sensor is located up at the exhaust manifold(s) and the other sensor is located down at the catalytic converter. On other vehicles, both sensors are located down at the catalytic converter.


This is the upstream sensor




This is the down stream sensor

usualy they are locate in 1 of 2 places right in the exhaust manifold or it will be in the down pipe near the top

Maybe this will help . although this is from a 1997 Caddy.


Cadillac DeVille Engine Coolant Temperature (ECT) Sensor Location