Skip the auto shop - Our mechanics make house calls

Q: O2 sensor on exhaust manifold...is it upstream or downstream...09 Nissan Altima

asked by on

Service Engine Soon light is on and I am getting the Catalytic converter replaced. I just need to know which O2 sensor to buy ? Upstream or downstream ?

My car has 21400 miles.
My car has an automatic transmission.

A: Hey there, thanks for writing in about your...

Hey there, thanks for writing in about your 2009 Nissan Altima. The downstream O2 sensor is the sensor used for catalyst efficiency. It is not the one in the manifold but the one after the converter. If you need help with an oxygen sensor replacement, our technicians can come to your location to install the correct the part.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: White smoke at starup on a '98 Maxima

That is a classic sign of the blowing head gasket. What you'd want to do first is watch my video "how to tell if your head gasket is blowing." If it is, you'll need to figure out whether you'd like...

Q: Battery keeps getting drained while the car is off during the night

Hello there, thanks for writing in about your 2009 Chevrolet Aveo5. Batteries that drain overnight are not uncommon. This is called a parasitic drain and can have many different causes. The most likely are any aftermarket electrical accessories, such as...

Q: Ac not working properly

This is likely coolant temp sensor relay problem as this is what controls the fan turning on and off. The AC simply puts an added load on the vehicle's engine, but is not connected to the fan. I would suggest...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...