NOX Sensors I get the P20EE CEL / code?

You're code is telling you which bank it is. P20EE means SCR NOx Catalyst Efficiency Below Threshold (Bank 1). A couple questions as to why they are going bad:

1. What brand did you replace with?
2. Are there any other codes?
3. How old and what quality is DEF fluid?
4. Do you have any exhaust leaks?

Thank you for the response.

1. GM Genuine ACDelco
2. Just after I submitted the first post, I got code P249D
3. New flud, checked concentration @ 32.5%
4. No exhaust leaks

The P20EE/P249D/P249E codes. P249D means the closed-loop reductant system has reached its correction limit because it believes DEF flow is too low. You need to test the DEF dosing system, including inspection of the DEF injector and a reductant injection quantity test. I would not replace either NOx sensor at this point. Also can I ask for you to send short video of the engine at idle from under the hood. If the engine is making excessive noise these codes will come up as well. I the engine sounds okay I would remove and inspect the DEF injector and the injector opening in the exhaust for crystallized DEF deposits.

The engine at idle seems normal. I have an injector on order, and will replace if necessary when I inspect the current one on Monday. I'll update you on how it goes. Any idea how to get the DEF injector to last longer? This will be the 4th one, and the vehicle only has about 72k miles..

Here is what GM says:


DEF naturally crystallizes when the water portion evaporates, so deposits can form around the injector nozzle. Some crystallization does not necessarily mean the injector has failed. In fact, GM's diagnostic information indicates that deposits can sometimes be cleared by operating the injector during the quantity-test procedure.


When you remove it Monday, don't throw the old injector away. If you can, take a picture of the injector tip and the opening in the exhaust pipe before cleaning anything. Post those pictures here and we can see what the deposit pattern looks like.

Ok, will do. Thank you for the quick response and info.

np, let us know what happens.

Here are the pictures of the exhaust opening and the injector tip.

I cleaned the opening,and installed the new injector.

I cleared the codes, and did a DPF service regen.

I'll take it for a test drive later today...

I took it for a test drive. As soon as I started the vehicle, the CEL came back on. It still has the same code P249D saying pending and permanent. Will it go away once all the monitors set? I tried driving it by following the procedures to set the monitors, but so far, the CEL is still on, and most of the monitors have not set yet. I will try again tomorrow. Is there anything else that I should be trying?

I took it for another drive. Tge CEL turned off. I scanned it, not all monitors are reset, and now the only code that id left is P249D "stored". Is there anything else that I should do (clear the stored code?) Or am I done, and I should just leave it alone?

Yes, clear the stored code and the problem should be fixed :)