The service engine soon light came on. Diagnosed with PO411 code. Dealership replaced diverter valve. Two more times after that, light came on again. They replaced the air valve solenoid. Car is spark knocking really bad. They are now talking about the ERG valve. Just looking for answers. Thanks.

It means time for a service.
Take it to your Nissan dealership for service.

Error Code: P0154
Description:
Heated Oxygen Sensor (HO2S) 1 , Bank 2 - No Activity Detected
Problem areas:
- Wiring.
- Open circuit in signal wire, between Heated Oxygen sensor 1, Bank 2 and ECM. (Must check and confirm)
- Heated oxygen sensor (HO2S).
- Engine control module (ECM).

Goolge the codes
OBD PO107
OBD PO122
2003 Mitsu Daimante PO411
etc
What you should do -- is never go to a dealer
Local shop down the street

Follow the link for help with this fault code P1405 Ford DPF EGR Sensor Circuit High Voltage Detected

I suggest you replace the EGR valve position sensor.

Yes, it's possible, but the valve can be tested rather than just replacing it, as there are other possible reasons for the knocking. Knock can also be caused by bad knock sensors. They are not troubleshooting properly. These parts should be tested before replacing. What is the current trouble code?

The P0410 code refers to the emissions system.
The AIR pump puts air to the exhaust to lower emissions. It takes in outside air and pumps it through two one-way check valves into each bank of the exhaust.
About 90% of the time that this code is set, the one-way check valves have worn out or failed and allow water (which occurs naturally in the exhaust) back into the pump. In any cold climate, especially in climates with higher humidity, this water may be more excessive. The water partially fills the AIR pump, it can then freeze. When the PCM commands the pump on, if the pump is frozen it cannot turn, thus overloading the circuit and "popping" the fuse.

In here you can find the Trouble Codes List:
The CODE mean P0411 Secondary Air Injection System Incorrect Flow Detected

Good luck!!!

i would go to autozone if it is for egr valve then it is actually the dpf sensor the other codes are straight forward they will check them for free

the light will keep coming on until u have whatever electronic engine control problem u have fixed, each time the light comes on it sets a trouble code in the memory of the computer (called the PCM), have it tested for that code and get back to me.

Ok, when the service engine light is illuminated, this Will represent a failed sensor or a malfunctioning cpu that will need to be diagnosed by a service tech. this light has a trouble code that will have all information that you will need to fix what the light is signaling at this time. you will need to take the vehicle to a mechanic or the dealership so they can connect the diagnosis cpu to your in Car cpu port. this diagnostic cpu will download the actual description of the issue at hand and , it Will direct you to the location of the problem with this engine as well.

In most cases, it will be a failed sensor of some sort.

P0456 = EVAP Emissions Control System Leak Very Small

Is the gas cap on tight or is the seal damaged? If it needs replacement, get it from the dealer.