P20EE on Chevrolet
SCR NOx Catalyst Efficiency Below Threshold
P20EE on Chevrolet vehicles indicates scr nox catalyst efficiency below threshold. Au7o has documented this code across 2 Chevrolet models — most commonly on Colorado, Silverado 3500HD. This is a diesel emissions code meaning the Selective Catalytic Reduction (SCR) catalyst on Bank 1 is not cleaning up exhaust as well as it should. The SCR system sprays Diesel Exhaust Fluid (DEF) into the hot exhaust to convert harmful nitrogen oxides (NOx) into harmless nitrogen and water; NOx sensors before and after the catalyst tell the computer how well it is working. When the measured efficiency falls below the required threshold, this code sets. Because it is an emissions-protection code, it often triggers warning lights and can lead to reduced power or a speed limit (a 'derate') if left unfixed. Typical repair costs on Chevrolet range from $200 to $2,500, depending on the specific model and root cause.
Common Causes of P20EE
- •Poor quality, contaminated, or wrong DEF fluid
- •Faulty or clogged DEF injector/dosing valve
- •Failed upstream or downstream NOx sensor
- •Degraded or failed SCR catalyst
- •Exhaust gas temperature sensor fault affecting dosing
- •Exhaust or DEF line leak
- •DEF line/heater problems (crystallization or freezing)
P20EE on Chevrolet by Model
Chevrolet Colorado(1 issue)
- Diesel Emissions System Issues (DEF/DPF)2016-2023
The 2.8L Duramax diesel can experience issues with the emissions system including DEF (Diesel Exhaust Fluid) quality sensors, DPF (Diesel Particulate Filter) regeneration problems, and NOx sensor failures. These can cause reduced power mode and check engine lights.
Chevrolet Silverado 3500HD(2 issues)
- DEF System Malfunction and Reduced Power2011-2025
Diesel exhaust fluid (DEF) system components fail causing "Service Exhaust Fluid System" warnings and eventual speed limiting to 65 mph then 5 mph. DEF injector, heater, or quality sensor most common failure points.
- DEF System and SCR Catalyst Failures2011-2025
The Diesel Exhaust Fluid (DEF) system is plagued with issues including DEF tank heater failure, injector clogging, quality sensor malfunctions, and SCR catalyst degradation. Any failure triggers a countdown timer that eventually limits the truck to 5 mph if not addressed. The system is sensitive to DEF quality and crystallization.
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View P20EE across all makes →Frequently Asked Questions
What does P20EE mean on Chevrolet?▼
P20EE stands for "SCR NOx Catalyst Efficiency Below Threshold." This is a diesel emissions code meaning the Selective Catalytic Reduction (SCR) catalyst on Bank 1 is not cleaning up exhaust as well as it should. The SCR system sprays Diesel Exhaust Fluid (DEF) into the hot exhaust to convert harmful nitrogen oxides (NOx) into harmless nitrogen and water; NOx sensors before and after the catalyst tell the computer how well it is working. When the measured efficiency falls below the required threshold, this code sets. Because it is an emissions-protection code, it often triggers warning lights and can lead to reduced power or a speed limit (a 'derate') if left unfixed. On Chevrolet specifically, this code is documented across 2 models.
What causes P20EE on Chevrolet vehicles?▼
Common causes on Chevrolet: Poor quality, contaminated, or wrong DEF fluid, Faulty or clogged DEF injector/dosing valve, Failed upstream or downstream NOx sensor, Degraded or failed SCR catalyst, Exhaust gas temperature sensor fault affecting dosing. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P20EE on a Chevrolet?▼
Repair costs on Chevrolet range from $200 to $2,500, depending on the specific model and root cause.
Which Chevrolet models have P20EE documented?▼
Au7o has documented P20EE on 2 Chevrolet models: Colorado, Silverado 3500HD.