Postby smj999smj » Thu Oct 23, 2014 2:26 pm
Not necessarily. If the sensor had an open circuit, or was shorted, it would likely set a trouble code. If it was reacting slowly or reacting with a lean or rich shift, probably not. You have to remember we're dealing with OBD I; it was state of the art when it came out, but a bit crude by OBD II standards. If you think the oxygen sensor is original, then it's time for a new one being almost 20 years old. I would also check the fuel pressure and make sure it's within spec. If the regulator is bad, it will cause the excessive fuel pressure and a richer mixture. The knock sensor will not cause excessive emissions. When it detects a knock, the ECM will read the signal and retard the timing slightly to try and prevent engine damage. Since your emissions are so out of whack, it could be setting a knock sensor code in reaction to the problem that is causing the high emissions. So, I would fix that problem first, erase the code, then see if it returns. The knock sensor is under the intake manifold, so it's no easy job to replace. Many purchase a 95 Maxima knock sensor and subharness and relocate the sensor to the top side of the intake, rather than teardown the top of the engine.