LML P20EE: SCR NOx Catalyst Efficiency Below Threshold Bank 1

[13dmax83]

2013 GMC Sierra Duramax with 100,000 miles. Went on vacation to Florida from East Texas pulling my 30 TT. All ran fine and pulled great. On the trip home on Friday the engine light came on and stayed on the whole trip. Once we got home and got unhooked and unloaded, the engine light went off. I went to Autozone and had the code pulled and it was P20EE: SCR NOx Catalyst Efficiency Below Threshold Bank 1. I am knew to diesel and duramax. Anyone have any ideas? Dealer isnt open today but i will be going in tomorrow to talk to them and see what they say

 

[onebaddmaxxx]

Likely one or both of the nox sensors are bad if u have anyone with a good scanner snap on tech2 etc, go on a drive with the engine up to temp.....perform a wide open throttle pass from 30-70mph and let off. Do not touch the brakes and monitor nox sensor 1 and nox sensors 2. You will be looking at readings showing data in PPM. After you let off, both values should drop under 5ppm. If either or both do not, that corresponding sensor is bad. When I worked at the dealer I had so many of the p20ee and p204d codes come in ALWAYS was a bad nox sensor!

After replacing sensors, a def quality test must be performed.

 

[13dmax83]

Are these sensors something that can be done by myself or does the dealer have to do this? And as far as the DEF quality test, what does that consist of? And im guessing that has to be done by the dealer?

 

[onebaddmaxxx]

You can change the nox sensors they take about 5 minutes each but the quality test needs to be performed by someone with a scanner with capabilities.

 

[Ron Nielson]

After replacing sensors, a def quality test must be performed.

I'm interested in knowing what % of time the def failed the quality test, if you recall.