I recently changed my timing chain tensioners on my 2005 Altima VQ35 and now I get the P0011 and P0021 codes. I've reset them and changed the oil but they keep coming back. I need to smog my car within the next few days and I can't figure out what it is.

code p 0011 refers to cam shaft (CMP) intake /left/front bank 1--timing over advanced/ system performance===causes ---valve timing---engine mechanical fault--- CMP actuator---wiring
if you have not worked on the head ot replaced the timing belt/ chain the problem most likely is in the wiring or the CMP unit
code p 0021 refers to CMP intake /left/front, bank 2 timing over advanced / system performance === causes --same as p 0011 and the reasoning is the same but more so on the wiring and connections

Take it back but go to the dealer, these are all related codes and need a Subaru expert to diagnose the cause.

Well code 11 is for a problem with the cam sensor signal on bank one and code 21 is the same issue with the sensor on bank two.
Its possible the timing belt has jumped.

the codes p0011 and p0012 both refer to camshaft (CMP) intake left front bank 1 timing over advanced / system performance-- among others -- camshaft timing (valve timing). I would have the valve timing rechecked as it appears that it is not right Probably a tooth out on both cam shafts.

Check you previous request. If Nissan won't help go to a good mechanic with Nissan experience as the company will not be willing to do rework for their mistake. The CPU is telling you by fault code what the problem is . If I am right and it is the timing I suggest that you find a good legal counsel and have Nissan pay all your repair bills form when they did the job.

The 1.8 and the 2.8 motors are common to throw those codes when the timing chain adjuster fails. the guides (shoes) start to break apart, take the valve cover off and check the tensioner

P0011 "A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)
P0021 "A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 2)

P0011 - "A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)

What does that mean?
A code P0011 refers to the VVT (variable valve timing) or VCT (variable camshaft timing) components and the car's PCM (powertrain control module, also called an ECM). That consists of a few different components but the P0011 DTC specifically refers to the camshaft (cam) timing. In this case, if the cam timing is above a set limit (over-advanced), the engine light will be illluminated and the code will be set. The "A" camshaft is either the intake, left, or front camshaft.

Potential Symptoms:
Most likely a P0011 DTC will result in one of the following: hard starting, poor idle, and/or stalling. There are potentially other symptoms as well. Of course, when trouble codes are set, the MIL (malfunction indicator lamp, a.k.a. the check engine light) illuminates.

Causes:
A P0011 DTC trouble code may be caused by one or more of the following:
* Incorrect camshaft timing
* Wiring problems (harness/wiring) in intake timing control valve control solenoid system
* Continuous oil flow to VCT piston chamber
* Failed timing valve control solenoid (stuck open)

Possible Solutions:
This DTC code is a result of a mechanical fault of the VCT unit or related components, so there is no need for electrical diagnosis. Refer to vehicle specific repair manual to perform component tests for the VCT unit. Notes: Dealer techs have advanced tools and the ability to follow detailed troubleshooting steps, including the ability to test components using a scan tool.

Other related DTCs: P0010 - P0011 - P0012 - P0020 - P0021 - P0022

Hope helps (remember rated this).

The timing chaing noise is very common on almost all v6 nissan engines. There is a significant difference for the maxima's though.

Timing chain noise is very common and it is the result of the secondary timing chain tensioners. They often stick and put too much tension on the chain and the plastic guides for the tensioner wear down to metal and that is the noise you hear.

At Nissan, I have performed this replacement many times and I suggest you take it to the dealership to have it fixed.