I did a quick search and didnt find an immediate answer to my question so I appologize if this is a repost. My Max has just hit 100000 and I have had a po420 or whatever the o2 sensor code is. I want to replace all of my sensors. Where do I go? How much? How many? etc. TIA

 

A p0420 is a cat function code. If you have only that code the consensus is that it is most likely the cat itself.

If you want to replace the sensors, it depends on how much you want to spend verses how reliable the new sensors are going to be. I had a shop refuse to install anything other than oem sensors unless I waived their standard guarantee for the work. Perhaps they were snowing me, but I don't have any codes and I do have their guarantee.

 

I have a high flow cat so I am thinking maybe a O2 sim but I would think I should change the sensors soon.

 

It all depends whether you have to pass an emissions test. Mine was just an ECM query without even running the engine so the ECM had to be clean.

In terms of the engine, I believe the timing and injectors just look at the front o2 sensors for reference. You'll throw a p0420 when the front and rear sensors don't add up right in the ECM.

 

would a bad O2 sensor make the RPM bounce when being held at about 2k? Mine has does this since I bought it. New MAF and it still does it? Any help? I was told it might be the O2 sensor.

 

^^^ doubt it. Especially since you're not getting a bad o2 sensor code. You have an auto or manual transmission?

 

its an auto and I have only noticed the bounce in P or N. Never while driving.

 

So you're in Park and trying to keep a steady 2k rpm and the revs bounce up & down? And this is before and after you got the cat code? No problems when driving? No other issues? If so, how important is it to you to find out why it's happening?

Not wanting be insulting with these questions, but I'm wondering if it's worth the worry?

 

My maxima just hasnt been running like it used to. So I was trying to narrow it down. Thought it might help me out.

 

Spark plugs been changed? TB cleaned? Many 2k owners say that a new MAF makes a big difference.

I've got a 2k with 93k miles which is running just fine. I had to replace rear o2 sensors and flash the ECM to pass emissions recently, but it made no difference in performance.

 

P0420 is the code for your rear precat, not for O2 sensors, although some people have apparently fixed it by replacing their rear bank secondary O2 sensor.

From the FSM, the possible causes for a P0420 are:

- Three way catalyst (Manifold)
- Exhaust tube
- Intake air leaks
- Injectors
- Injector leaks
- Spark plug
- Improper ignition timing

 

I'm one of them, but I also had o2 error codes.

 

- Three way catalyst (Manifold)
Leand condition causing damage to 3 way catalyst.
The voltage reading in the manifold is not within spec from the sensor to the ECM. This scenario is true for ALL the following items (Senser V does not meet spec for ECM) and will cause the code.


- Exhaust tube
Exhaust leak, too much air in exhaust stream. (supposed lean condition)

- Intake air leaks
Lean condition, air may be entering AFTER the MAF, therefore not being metered, in return, no fuel being compensated for extra air resulting in a lean condition.

- Injectors
There is not enough fuel being pumped into the cylinders, or there is excess, therefore causing a lean/rich condition.

- Injector leaks
Read above.

- Spark plug
The spark plug is not functioning therefore allowing excess unburned raw fuel to enter the exhaust tract.

- Improper ignition timing
Spark plug not firing at the correct time, therefore leading to the above statement.

 

With those conditions you will almost always get another code as well, like a misfire or o2 code.

 

That secondary code coupled with my post should help pin point the problem further.