Experiencing check engine lights can be frustrating, especially when you’re trying to pinpoint the issue. Recently, I encountered emission problems with my 2017 Chevrolet Colorado Duramax (around 55k miles, all stock components), and the troubleshooting process led me to understand more about codes P20EE and, crucially, P11d5. I’m sharing my experience hoping it helps others facing similar diagnostic dilemmas.
Initially, the check engine light illuminated, and a scan revealed the P20EE code: “SCR NOx Catalyst Efficiency Below Threshold Bank 1”. Shortly after, another code appeared: P11D5 “NOx Sensor 2 Exceeded Minimum Learning Limit”. Alongside these codes, I noticed a decrease in fuel economy and a less frequent diesel particulate filter (DPF) regeneration cycle – dropping to about 330 miles between regens, down from the usual ~430 miles.
My first step was to seek advice. The dealership where I purchased the truck casually suggested cleaning the Mass Air Flow (MAP) sensor. Online forums, particularly a Facebook group dedicated to Colorado owners, leaned towards replacing the NOx sensors. While I plan to clean the MAP sensor when I get a chance and have acquired a spare NOx sensor #2, I decided to take it to my local Chevrolet dealer for a professional diagnosis.
I informed the local dealer about the P20EE and P11D5 codes. Their diagnosis revealed that the Diesel Exhaust Fluid (DEF) pump was receiving power but failing to function correctly, specifically failing a DEF quantity test. They recommended replacing both the DEF pump and the DEF module.
The parts quoted were:
- DEF Pump (Part #84526247): Rock Auto Price $443.79, Chevrolet List Price $1,077.99
- DEF Module (Part #39153712): Rock Auto Price $131.79, Chevrolet List Price $348.99
The dealership proceeded with replacing these components. They confirmed the presence of the P11D5 and P20EE codes and explained their findings: the reductant pump wasn’t generating enough pressure to activate the reductant injector and heat up the Selective Catalytic Reduction (SCR) converter. This lack of heat was causing the P20EE code. Consequently, they replaced both the reductant pump and its controller (DEF module). Additionally, they added 2 gallons of DEF, priced at a steep $12.95 per gallon, significantly higher than my usual purchase price.
Unfortunately, due to work commitments, I couldn’t undertake this repair myself. While I negotiated a slightly better price with the dealer than the initial excessive Chevrolet list prices, the final bill still exceeded $1,700. I also wasn’t thrilled about them adding DEF, as I intentionally kept my tank half full for winter to avoid potential freezing and expansion issues in sub-12°F temperatures.
Adding to the frustration, the emissions warranty did not cover these repairs. My research indicated that my state follows California emissions warranty regulations, which, for these components, only extends to 5 years or 50,000 miles. Being slightly over the mileage limit, I was responsible for the entire expense.
This experience has highlighted the vulnerabilities within the emissions system of this truck. The exorbitant list prices for OEM parts from GM, particularly for emissions-related components, have significantly impacted my perception as a Chevrolet customer. Dealing with codes like P11D5 and P20EE can be costly, and understanding the potential causes and fixes is crucial for Chevy Colorado Duramax owners.
