Sensor-tive issues, o2 and knock sensors

[VinnyVinnVinn]

Hi everyone, I just accquired a 2000 Subaru Legacy Brighton and I am having a few issues with it.  The check engine light is on and when I pulled the codes I came up with P0325 Knock Sensor no. 1 Circuit malfunction P0420 Catalyst Efficiency Below Threshold and P0133 02 Sensor Slow Response.  I am assuming that the two sensor related problems would trigger a P0420 so I should resolve these first.  What I wanted to know is if there is a difference between the various replacement sensors.  In otherwords, should I buy straight from the dealer or will a Bosch sensor from autozone or napa be good enough?  Also, is the slow response from the o2 sensor caused by a faulty sensor, or could it be caused by something else like a loose wire or bad connection or improper fuel trim etc?  Thanks, I look forward to your help and answers and I assure you, I will probably have many more questions.

[Fairtax4me]

A lot of people use knock sensors from EBay/Amazon with good results.

 

O2 sensor slow response is usually the sensor (happens when they get old), but it can be caused by other problems.

 

Bosch O2 sensors will work fine. Do not get the universal fit type. Check the shape of the connector on your sensor (check carefully because some differences are minor), and compare to new sensors before you order.

 

There are two or three different sensors that your car could have, and they work slightly differently than one another. Getting the wrong type of sensor will lead to more (worse) problems.

[VinnyVinnVinn]

Thank you Fairtax4me, just curious but what is the difference between the different sensors, how do I tell them apart?

[Fairtax4me]

Internal differences mostly. Some have to have a reference voltage from the ECU, which affects the output of the sensor. And of those there are 3 or 4 different designs which all use different reference voltages. Others create the voltage in the sensor. The outer cases can be slightly different, but not different enough to tell them apart unless you're the engineer that designed the sensor. The fun part is that just about all of them have 4 wires! So there's really no way to tell unless you KNOW which one you need.

 

Pay close attention to the plug, because that's how the manufacturer keeps you from plugging in the wrong one.