View on LOZ Suggested Retail: $176. 12669595 NOx Sensor Downstream Nitrogen Oxide Sensor for Chevy GMC Duramax 6.6L Diesel 2010-2014 12671388 5WK96645H. NOx sensors monitor the level of nitrogen oxide emitted by a diesel vehicle to ensure compliance with emissions regulations and can also contribute to better fuel economy and cleaner air. When the NOx sensor isn't sending data and information to the ECU, the ECU can't tell the right amount of fuel to send to the engine, and in most cases, it sends incorrect fuel mixture and air-to-fuel ratio which leads to increased fuel consumption.. 7 CALENDAR DAY FULL REFUND GUARANTEE (FROM PRIMARY PICKUP DATE) ON THIS ITEM IF ANY ISSUE IS FOUND THAT WAS NOT DESCRIBED/PICTURED. 7 CALENDAR DAY STORAGE (FROM PRIMARY PICKUP DATE) IS ALSO AVAILABLE. THE PRIMARY PICKUP DATE IS THE DAY AFTER THE AUCTION ENDS. SEE NOTES TO BIDDER, IN AUCTION DETAILS, AT THE TOP OF PAGE 1 FOR MORE INFO.