Fix P20EE: Mechanic’s solutions that WORKED

The code P20EE: “NOx Catalyst Efficiency Below Threshold Bank 1 Catalyst 1” indicates a problem with the NOx (Nitrogen Oxide) reduction system in the vehicle’s exhaust, specifically that the efficiency of the NOx catalyst is below the expected threshold.

P20EE quick overview

Meaning	P20EE: “NOx Catalyst Efficiency Below Threshold Bank 1 Catalyst 1”
Is it serious?	Yes, it is important as it relates to the vehicle’s emissions control system and can impact its environmental footprint and compliance with emissions regulations.
Possible causes	– Faulty or inefficient NOx catalyst – Malfunctioning NOx sensors – Issues with the DEF (Diesel Exhaust Fluid) injection system – EGR (Exhaust Gas Recirculation) system malfunctions – Engine running issues leading to incorrect exhaust composition
How to diagnose?	Inspect NOx Catalyst: Check for damage or signs of inefficiency. Test NOx Sensors: Verify their functionality and accuracy. Evaluate DEF System: Ensure proper operation of DEF injection. Check EGR System: Look for any issues affecting EGR operation. Assess Engine Performance: Ensure the engine is running properly, as this can affect exhaust composition.

In simple terms, the P20EE code means that part of your vehicle’s system that reduces harmful emissions isn’t working as well as it should. This could be due to a problem with the sensors that monitor emissions, the fluid used to help reduce emissions, or even an issue with the engine itself. It’s important to fix this to ensure your vehicle remains environmentally friendly and complies with emission standards.

How to fix P20EE – learn from mechanics

I looked into P20EE service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Ram

Vehicle Information

• 2013 Ram 5500 ST, 6.7L

Issue + Repair History

• MIL (Malfunction Indicator Lamp) on
• Codes: P2201 (NOx Sensor 1 Circuit/Range Performance), P229F (NOx Sensor 2 Circuit/Range Performance), P20EE (SCR NOx Catalyst Efficiency Below Threshold), P207F (Reductant Quality Performance)
• Previous codes (resolved after reflash): P249E (Closed Loop Reductant Injection Control at Limit – Flow Too High), P1C54 (SCR NOx Catalyst Missing)
• Reflashed ECU for TSB 18-022-16
• Installed two new NOx sensors

Other OBD2 Codes + Test Results

• DEF fluid test: 33%
• DEF dosing test: 85-115ml (all tests between 100-105ml)

Community Suggestions

• Check connection and circuit before buying new sensors
• Consider potential DEF fluid issues; drain and refill with new DEF
• After road test, check for pending NOx system codes
• Complete any open recalls, especially one for replacing the SCR Catalyst
• Extended highway test drive for successful SCR catalyst monitor test

Final Fix

• Replaced both NOx sensors
• Found a recall (code U84) for SCR catalyst replacement, released truck to owner for recall service
• No update on whether recall fixed the issue

Case #2: Volkswagen

Vehicle Information

• 2010 Volkswagen Touareg TDI, 3.0L Adblue

Issue + Repair History

• MIL (Malfunction Indicator Lamp) on
• Code: P20EE (Converter Efficiency)
• Adblue injector clicks but does not dispense fluid
• Exhaust fluid recently replenished

Community Suggestions

• Check if there’s pressure in the exhaust fluid line
• Inspect the injector inlet for crystallization or plugging
• Use a scan tool to command the pump on and monitor exhaust fluid pressure
• Ensure DEF (Diesel Exhaust Fluid) pump and heater assembly in the tank are functioning
• Actuate the DEF pump to check pressure
• Consider the possibility of a faulty NOx sensor in the rear catalytic converter

Final Fix

• Replaced Adblue injector
• Performed Basic Settings 170 test on the Adblue system, which cycled the new injector successfully, showing a nice cone shape and adequate flow

Case #3: GMC

Vehicle Information

• 2011 GMC Sierra 3500 HD SLE, 6.6L

Issue + Repair History

• MIL (Malfunction Indicator Lamp) on
• Main concern: Outside Air Temperature Sensor (OAT) reading -40 degrees
• Sensor resistance/temperature checked and okay
• Good sensor signal (5V) and ground (5 ohms or less)
• Cleared HVAC code B0158, HVAC module then read correct temperature
• ECM still showed OAT as -40 even after HVAC update

Community Suggestions

• Let the vehicle sit for 6+ hours or overnight for ECM to reset ambient temperature
• Check if OAT sensor is located in the outside rearview mirror, especially if mirrors were changed
• Ambient Air Temperature is an ‘inferred’ temperature based on various factors, not just one sensor
• Some scan tools have a special function for OAT instant update

Final Fix

• Replaced the ambient air temperature sensor after inspecting the wiring harness
• The ambient temperature in ECM updated overnight
• Addressed the issue of code B0158 (short to ground) with the sensor replacement

Other Codes Mentioned

• P046C (EGR Sensor Performance)
• P20EE (NOx Catalyst Efficiency Below Threshold)
• P0401 (Exhaust Gas Recirculation (EGR) Flow Insufficient)
• B0158 (Outside Air Temperature Sensor Circuit Short to Ground)

Case #4: BMW

Vehicle Information

• 2009 BMW X5 xDrive35d, 3.0L

Issue + Repair History

• Excessive emissions
• Previous issue: loose EGR cooler

Community Suggestions

• Check the NOx sensor circuit using the wiring diagram, as the sensor might be faulty
• Contact dealer regarding parts warranty, especially for NOx sensors and catalytic converters
• Access BMW technical information via bmwtechinfo.com for detailed repair instructions and diagrams
• Consider if the vehicle is still under emissions/powertrain warranty

Final Fix

• Blown EGR cooler gasket caused air to enter the exhaust stream, affecting sensor readings
• Repairing the EGR cooler gasket resolved the issue

Computer Codes & Descriptions

• P20EE – NOx Efficiency
• P2201 – NOx Sensor Circuit
• P1515 – Unknown code (BMW specific)

Case #5: Chevrolet

Vehicle Information

• 2012 Chevrolet Silverado 2500 HD LT, 6.6L

Issue + Repair History

• Initially, all listed codes present
• DEF pump found inoperative; pump and injector replaced, did a regen
• Came back with P24A0; EGT #4 sensor constantly reading 1800*
• Replaced all 4 EGT sensors, reflashed computer
• Issue persisted, P24A0 again with EGT #4 showing 1800* KOEO
• Checked wiring, replaced computer
• Returned with P24A0 once more

Community Suggestions

• Remove the indirect injector from the exhaust and test for fuel leakage or operation
• Check if the P24A0 issue is related to a faulty indirect fuel injector
• For NOx sensor #2 related codes, consider replacing the sensor
• Verify if the new ECM corrected the EGT #4 issue; if not, it might be a scan tool issue

Final Fix

• Replaced the “9th injector” (indirect fuel injector) which was clogged

Computer Codes & Descriptions

• P24A0: Closed Loop Diesel Particulate Filter (DPF) Regeneration Control At Limit – Temperature Too Low
• P22A1: NOx Sensor 2 Circuit High Voltage
• P20EE: NOx Catalyst Efficiency Below Threshold
• P2BAD: Exhaust NOx Concentration High – Unknown Reason
• P22A0: NOx Sensor 2 Circuit Low Voltage