When your 2016 Chevrolet Colorado Duramax diesel sets a P20EE code with a DEF (Diesel Exhaust Fluid) warning, the emissions system has detected that the DEF quality doesn't meet specifications. This warning should be addressed promptly to avoid the vehicle entering reduced power mode or becoming immobilized.
Understanding P20EE
P20EE indicates the Selective Catalytic Reduction (SCR) system has determined the Diesel Exhaust Fluid quality is below the required threshold. The DEF tank contains sensors that monitor urea concentration. DEF that has been diluted, contaminated, or degraded triggers this code.
DEF System Function
The Colorado Duramax uses DEF (a urea-water solution) injected into the exhaust to reduce NOx emissions. The SCR system requires DEF with 32.5% urea concentration to function properly. The PCM monitors DEF quality and triggers warnings if the concentration is wrong, which prevents proper NOx conversion.
Common Causes
Diluted DEF from water contamination—never add water to DEF. Degraded DEF from heat exposure or age—DEF has a limited shelf life, especially in heat. Wrong fluid added to the DEF tank. DEF quality sensor failure providing false readings. Contamination of the DEF system from improper handling.
Consequences of Ignoring
GM's emissions system includes escalating penalties for DEF issues. Initial warnings allow continued operation. Ignoring warnings leads to reduced power (speed limited). Eventually, the vehicle may limit starting to 5 mph until the DEF system is corrected. This is designed to ensure emissions compliance.
Diagnostic and Resolution
If you've recently added DEF, verify it's actually DEF (not water or other fluid). Check DEF expiration date and storage conditions. Drain and replace the DEF if contamination is suspected—this often resolves the issue for $50-$150. If fresh, proper DEF doesn't clear the code, the quality sensor may need replacement at $300-$600. A complete DEF system flush may be required for severe contamination.