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oxygen sensors(O2S) are located after the cat converters
heated oxygen sensors (HO2S) are located in the exhaust manifold/ exhaust pipe before the cat converters
they are different sensors performing different jobs so rich or lean problems will be the HO2S in the manifold
You need to follow your exhaust. You have two. One in the front and one in the back. All you do is plug one side into the electrical connector and the other side screws into the exhaust. You need to find out if it is the upstream sensor or downstream sensor before you change that one. The one in front is upstream.
Code PO 420 is telling you that the Catalyst System Efficiency
Below Threshold (Bank 1), so the Cat converter inst working as it should according the the vehicles computer. This can be caused from the converter going bad from age and use. Or it can also mean you have a failing rear oxygen sensor, because this sensor is instrumental in keeping track of what the converter is doing. If the car is driven on several short trips, and hardly ever driven on the highway, you may be able to burn the deposits out of the converter and restore its function. To do this you should drive it on the highway for at least two hours. After this have the light reset. If the code comes back then have the converter and oxygen sensor tested. Most shops will simply want to replace them and see if it fixes the problem. Don't fall for this, because it is expensive, and you don't need them changed unless they are bad. Get the converter tested and the oxygen sensor tested prior to replacement. The problem could be as simple as a bad electrical connection on the oxygen sensor, that is why I say have them tested.
B1S1 means first (upstream) , closest sensor to cyl. head , usualy at exhaust manifold.Bank 1 is cyl. head with cyl.#1 if you have V6 engine.
Best choice for brand - Denso.
They are two oxigen sensors. High and low, before you change any one of them, tray to take your car to autozone or napa. They can check it for you for free, and they can tell you which one you need to change.
both oxygen sensors are in the bottom of the car, before and after catlic converter. Make sure you left the car using hydraulic or mechanical jack and secure it with 2 stands. disconect the ox sensor and remove it from the exhaust pipe. Let me know if you still have any problem
Mass Air Flow sensor! Just remove your air filter cover. Go to Auto Zone and purchase some solvent. Spray past the air filter and it should correct the problem. If not, replace the Mass air-flow sensor. This is commonly mistaken for an oxygen sensor. Mine did this and I followed these steps and it fixed the light. BTW, the light stayed on for 5 years before I fixed it. Never hurt anything. It's normally something to do with emissions. Dummy lights. :)
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