2015 Audi Q7 - P20EE and AdBlue System Malfunction

Question

My Q7 just popped a 'No start in 200 miles' warning on the dash along with a P20EE (SCR NOx Catalyst Efficiency Below Threshold Bank 1). I already topped off the DEF/AdBlue fluid, but the countdown hasn't gone away.

I'm terrified of getting stranded. I've heard that if the DEF injector gets crystallized, it won't spray correctly, but I haven't pulled it yet. The car seems to run fine otherwise, no smoke or power loss. Is my expensive SCR catalyst toast?

RegenRogerD · Accepted Answer

✅ Confirmed fix: My DEF injector was completely encrusted in white urea crystals. I pulled the injector (it's right there in the exhaust downpipe, held by one clip) and it looked like a head of cauliflower.

I soaked the tip in hot distilled water for 20 minutes to dissolve the crystals, then reinstalled it. I also performed an 'Adaptation of SCR system' using VCDS. The NOx readings stabilized, the P20EE went away, and the no-start countdown reset. Always clean the injector before replacing the catalyst!

OwnerOpOlly · Answer

You likely have a failed NOx sensor. There are two of them (upstream and downstream). If the downstream sensor is reporting high levels of NOx even after a regen, it will trigger that countdown. You need to look at the live data for both sensors to see if the downstream is tracking correctly.

2015 Audi Q7 - P20EE and AdBlue System Malfunction

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