Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
Your car has a special filter that helps clean the air coming out of the engine. This filter isn't working as well as it should, so the car is warning you about it.
The Selective Catalytic Reduction (SCR) system reduces nitrogen oxide (NOx) emissions. This code indicates that the efficiency of the SCR system is below the expected threshold for Bank 1.
The P20EE code is triggered when the Engine Control Module (ECM) detects that the NOx reduction catalyst efficiency is below the required threshold for the SCR system on Bank 1. This typically involves the SCR catalyst not converting NOx into nitrogen and water effectively, which may be due to a malfunction in the SCR system or related components.
• Check Engine Light is on
• Reduced engine performance
• Increased NOx emissions
• Faulty SCR catalyst
• Malfunctioning NOx sensors
• Poor quality DEF (Diesel Exhaust Fluid)
SCR: Selective Catalytic Reduction - a system that reduces NOx emissions in diesel engines.
NOx: Nitrogen Oxides - harmful pollutants produced during combustion.
• Use an OBD-II scanner to confirm the code.
• Inspect the SCR catalyst for damage or clogging.
• Test the NOx sensors for proper operation.
• Replace the SCR catalyst if faulty.
• Replace or clean the NOx sensors.
• Refill DEF with high-quality fluid.
• OBD-II scanner
• Multimeter
• Wrench set
$500 - $2000
Moderate
• Ford F-250
• Chevrolet Silverado 2500
• Ram 2500
• Regularly check and refill DEF.
• Perform scheduled maintenance on the SCR system.
• Use high-quality DEF.
Emission Control System Issue
• Do not ignore the Check Engine Light.
• Schedule a service appointment promptly.
• Avoid driving long distances until repaired.
SCR system components may be covered under the vehicle's emissions warranty.
The P20EE code has become more common as emissions standards have tightened, requiring more efficient SCR systems.
Moderate – While the vehicle may still be drivable, it is important to address this issue to maintain emissions compliance and avoid further damage.
Driving with a malfunctioning SCR system may result in failing emissions tests and could lead to fines in areas with strict emissions regulations.
• Engine running at normal operating temperature
• Vehicle driven under various speed conditions
The SCR catalyst is located in the exhaust system, typically downstream of the engine and close to the NOx sensors.
Q: Can I drive my car with a P20EE code?
A: While the car may still be drivable, it's best to have it checked soon to avoid increased emissions and potential fines.
Q: What happens if I ignore the P20EE code?
A: Ignoring the code can lead to higher emissions, potential damage to the SCR system, and failing emissions tests.
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Universal · Digital multimeter
A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
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Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
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Fitment Required · Vehicle-fitment part
Relevant when catalyst-efficiency or emissions faults persist after proper diagnosis.
Catalyst-efficiency faults sometimes point toward converter problems after proper testing.
Catalytic converters are highly vehicle-specific and should not be purchased by code alone.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.