Nissan Repair: Mercury Villager / Nissan Quest, obd2 scanner, mercury villager

Question
QUESTION: I have a 2002 Mercury Villager and was told that it is the same as a Nissan Quest. I have two powertrain codes that I can not fix. I am a BMW technician and have my own OBD2 scanner. I have P0141, O2 sensor, bank 1 sensor 2. then P0325, Knock sensor.
I replaced the downstream O2 sensor and fault returned as well as the knock sensor. I did nothing to fix the knock sensor yet. I do not want to continue with this car as I am not specialized with it. I figure I will write to you.
Any ideas on this vehicle?

ANSWER: Kevin,

I would replace the knock sensor as the Villager/Quest is known to eat them around 80K miles or anything over this.  The oxygen sensor could be caused by old spark plugs.  Also, with Nissan's it is good to replace all the oxygen sensors.  Yes, I know there is only one throwing a code.  But, they tend to go out close together.  The knock sensor could also be causing the issue since when the computer reads a defective knock sensor it runs a pre-programmed software fuel and timing map to keep from causing detonation.  Basically, over rich condition until the vehicle is repaired.

---------- FOLLOW-UP ----------

QUESTION: I have gone over the vehicle and I would appreciate if you could tell me where the knock sensors are at. I truely don't want to go in there guessing. Secondl I also noticed that this vehicle only has two O2 sensors not 4 as with typical dual bank systems. Lastly the O2 sensor was coming on long befoe the Knock sensor was, is it the knock sensor going out +/- 15k miles ago causing the issue after all?

Answer
Kevin,

The knock sensor is a vital component of the vehicle and for some reason Nissan has a problem with these going out.  The knock sensor senses spark knock and retards timing to keep from hurting the engine.  Replace this as soon as possible.

There has to be at least three oxygen sensors since there has to be one for each bank and one after the converter.  Since yours is an OBDII there has to be a sensor after the converter.  I would get a Haynes Manual for a diagram for your specific vehicle.