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AdBlue Warning and P20EE Code on 2019 Q7 3.0T TDI

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Rachel A. · rep 0 · May 22, 4:23 AM · 1 replies · solved · Question

Vehicle: 2019 Audi Q7 3.0T TDI Premium

Hi all,

I'm dealing with an AdBlue issue on my 2019 Audi Q7 3.0T TDI. I recently got an AdBlue warning message on the dash, saying I have a limited range before the car won't start. I topped up the AdBlue tank, but the warning hasn't cleared, and now the check engine light is on.

My OBD-II scanner is showing a P20EE code: 'SCR NOx Catalyst Efficiency Below Threshold (Bank 1)'. I know this is related to the Selective Catalytic Reduction system and AdBlue, but I'm not sure what specifically is causing it. I've heard these systems can be problematic.

Has anyone experienced this specific code or AdBlue system failure on their Q7 TDI? What was the fix? Is it usually a sensor, the injector, or something more serious? Any advice on troubleshooting or what to expect at the dealer would be helpful. Thanks in advance!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:23 AM

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ClearTheCode admin answer:

The P20EE code on your 2019 Audi Q7 3.0T TDI, combined with the AdBlue warning, indicates a problem with your Selective Catalytic Reduction (SCR) system's efficiency. This system is crucial for reducing NOx emissions in diesel vehicles, and a fault will often trigger a countdown to a no-start condition to ensure compliance with emissions regulations. Topping up the AdBlue tank is a good first step, but the code suggests a deeper issue.

Common Causes for P20EE and AdBlue System Faults:

  1. Faulty NOx Sensors: Your Q7 has upstream and downstream NOx sensors that monitor the SCR system's efficiency. If one of these sensors fails or provides inaccurate readings, it can trigger the P20EE code.
  2. AdBlue Injector Clogging/Failure: The AdBlue (DEF) injector sprays the fluid into the exhaust stream. If it becomes clogged with crystallized AdBlue or fails electronically, the correct amount of DEF won't be injected, leading to inefficient NOx reduction.
  3. AdBlue Heater Failure: The AdBlue system requires heating in cold weather to prevent the fluid from freezing. If the heater element in the tank or lines fails, the system won't function correctly, especially in colder climates.
  4. AdBlue Pump Failure: The pump is responsible for delivering AdBlue from the tank to the injector. A failing pump can lead to insufficient pressure or flow.
  5. Contaminated AdBlue: Using incorrect or contaminated AdBlue can damage the system components.
  6. SCR Catalyst Degradation: While less common on a 2019 model, the SCR catalyst itself can degrade over time, reducing its ability to convert NOx.
  7. Wiring or Module Issues: Faulty wiring to any of the SCR components or a problem with the SCR control module can also cause these issues.

When to See a Shop:

Given the complexity of the AdBlue/SCR system and the potential for a no-start condition, it's highly recommended to have your Q7 diagnosed by an Audi specialist or dealership as soon as possible. Specialized diagnostic tools are often required to properly test these components and clear the warnings.

Steps for Diagnosis:

  1. Full System Scan: A professional will use an Audi-specific diagnostic tool (like ODIS) to perform a comprehensive scan of the engine and SCR control modules. This will reveal specific fault codes related to NOx sensors, the AdBlue pump, injector, or heater.
  2. AdBlue System Test: The diagnostic tool can often activate and test individual components of the AdBlue system (pump, injector, heaters) to check their functionality.
  3. NOx Sensor Live Data: Monitoring the live data from the NOx sensors can help determine if they are providing plausible readings.
  4. Visual Inspection: Check for any leaks around the AdBlue tank, lines, or injector. Also, inspect the AdBlue injector for crystallization or blockages.
  5. Fluid Quality Check: While difficult without specialized tools, a shop might be able to test the quality of the AdBlue in the tank.
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