Want to know where the Knock Sensor and Oxygen Sensor are located in 1999 Nissan Altima GXE. Has anyone try to replace them? If yes, please share the procedure.

Thanks in advance!

The O2 sensors are located in the exhaust system, before the converter, and the Knock sensor is located near the center of the cylinder head (single white wire).

The O2 sensors and the Knock sensor, if failed or significantly out of range, will turn on the MIL or SES or Check Engine Light.

But they perform different functions. What type of symptoms are you experiencing?

(edit to line #1) The sensors aft of the converter are considered simple monitors and rarely fail as often as the forward O2 sensors, though both can.

Thanks for your reply! I have been finding my car's "service engine soon" lights on since a last couple of days and was doing some research as Mechanic's estimates are exorbitant. (>$900). But, I think this can be done at a much lower price. I went to Autozone and they found that the two sensors need replacement through the code-reading.

The O2 sensors are fairly straight forward as far as replacement goes.

The knock sensor can be a bear, though.

Maybe not something you'll neccesarilly want to do in the driveway, either one...

What were the codes Zone gave you?

The codes were P0141, P0325. I read somewhere that the knock sensor would not cause the SES lights on in Altima. Is this a fact with Nissan vehicles... But, if the diagnostics have shown this code, does the knock sensor necessarily need a replcaement. Can it be a kind of false alarm?

Correct. The P0325 will not turn on the MIL. And the P0141 is for the rear sensor heater circuit. Right now, I would address the rear sensor and clear the codes. If the KS is faulty, you'll need a code checker later, to find if it's come back.

That rear sensor is referred to as a catalyst monitor... meaning it checks to see if the converter is functioning. Just make sure if the sensor has to come out your wrench has a good bite on it or it may round off or strip. Good luck.

I own a 99' nissan altima. My check engine light is now displayed on the information console. I had a diagnostic check done to find that I need to change the rear O2 sensor. My question is do I also need to change the other o2 sensor located on the manifold?

stagordon, no you don't.