Experiencing car trouble can be frustrating, especially when warning lights pop up on your dashboard. For owners of the 2016 Chevy Colorado, understanding OBD2 codes is the first step towards diagnosing and resolving issues. This story recounts a personal experience with a 2017 Chevy Colorado Duramax, which should be applicable to similar models around 2016, encountering a “Poor Diesel Exhaust Fluid Quality” warning, and how an OBD2 scanner helped pinpoint and fix the problem.
After enjoying 91,000 trouble-free miles, my 2017 Chevy Colorado Duramax, in its original factory condition, presented its first real challenge. While driving to work, the ominous “Poor Diesel Exhaust Fluid Quality – See Owners Manual Now – 99 miles until speed limited to 65 MPH” message appeared, accompanied by the malfunction indicator lamp (MIL). This wasn’t entirely new; a similar incident occurred about five years prior, shortly after purchasing the vehicle while driving through remote Arizona. Back then, adding fresh DEF seemed to resolve the issue.
Hoping for a repeat of the past, I added a fresh jug of DEF to the tank, even though it wasn’t critically low. Unfortunately, this time the fault persisted, and the speed limitation kicked in. It was clear that a more in-depth investigation was needed.
Image depicting the old downstream NOx sensor removed from the 2016 Chevy Colorado after approximately 91,000 miles of use, highlighting component wear and tear.
This situation prompted me to finally invest in an OBD2 reader, something I had considered for a while. I opted for an OBDLink MX+ and used its companion app. By this time, the check engine light (CEL) was also illuminated. Scanning the system revealed two permanent OBD2 codes: P20EE, indicating “SCR NOx Catalyst Efficiency Below Threshold,” and P11DC, signaling “NOx Sensor #2 Current Fault.” Permanent codes are significant because they cannot be cleared manually until the underlying issue is fixed.
To understand the problem better, I monitored the readings from both NOx sensors, upstream (Sensor #1) and downstream (Sensor #2). Sensor #1 appeared to be functioning within normal parameters based on online research. However, Sensor #2 was erratic, fluctuating from zero to negative values and then spiking to readings two to three times higher than Sensor #1. These readings, combined with the P11DC code, strongly suggested a failure in the downstream NOx sensor. Online forums and communities corroborated that this sensor is a known point of failure, with some sources suggesting a lifespan of only 50,000 to 70,000 miles. My sensor had lasted 91,000 miles, which was somewhat beyond the average expected lifespan. A replacement sensor (P/N 24001920) was ordered from Rock Auto for $137 and thankfully was in stock.
Screenshot from the OBD2 app showing fluctuating readings and malfunctions during the diagnostic test on the 2016 Chevy Colorado, indicating potential sensor issues.
Image capturing the OBD2 diagnostic interface displaying error messages and sensor status during the troubleshooting process of the 2016 Chevy Colorado.
Display of OBD2 software interface during diagnostic testing of the 2016 Chevy Colorado, highlighting sensor data and system responses.
After a couple of days relying on my wife’s car, the new sensor arrived. Installation was straightforward, with the downstream NOx sensor being easily accessible. Following the replacement, I utilized the “Reductant System Warning Malfunction Service Bay Test” within the Gretio app (thanks to @Snipesy). Although the test seemed to extend beyond the expected 20 minutes, it eventually completed and, to my relief, passed. Immediately, the MIL, warning message, and speed limitation disappeared! Since the repair, I have driven approximately 60 miles, and the Chevy Colorado has returned to its normal operation.
Screenshot showing NOx sensor readings during the service bay test on the 2016 Chevy Colorado, illustrating sensor behavior and data trends.
The total cost for this DIY repair was quite reasonable: $150 for the OBDLink MX+, $137 for the NOx Sensor #2, and $20 for a year’s subscription to the Gretio app. This investment likely saved a significant amount compared to the potential cost at a dealership. While the Gretio app might not be strictly essential for code clearing, it expedited the process and provided valuable diagnostic capabilities. For $20 annually, it offers a cost-effective alternative to expensive scan tools or dealership visits, especially if used even once a year for vehicle maintenance and diagnostics.
Final diagnostic screen confirming successful completion of the service bay test and clearance of fault codes on the 2016 Chevy Colorado, indicating successful repair.
This experience underscores the value of understanding 2016 Chevy Colorado Obd2 Codes and investing in a good OBD2 scanner. It empowers owners to diagnose and potentially fix issues themselves, saving time and money while gaining a deeper understanding of their vehicle’s health.
