NOx Reset

📖 YOUCANIC Automotive Glossary

NOx Reset (NOx Sensor / SCR Catalyst Reset)

NOx Reset is a scanner function that clears and recalibrates the nitrogen oxide (NOx) monitoring system parameters, including the NOx sensors, SCR (Selective Catalytic Reduction) catalyst efficiency counters, and DEF dosing adaptation values. Modern diesel and some lean-burn gasoline vehicles use NOx sensors positioned before and after the SCR catalyst to measure the concentration of nitrogen oxide emissions in the exhaust — the upstream sensor tells the ECU how much NOx is entering the catalyst, and the downstream sensor verifies how effectively the SCR catalyst is converting NOx using the AdBlue/DEF injection. The ECU uses the ratio between upstream and downstream NOx levels to calculate SCR catalyst efficiency and adapt DEF injection rates for optimal NOx reduction.

The NOx Reset function is required after replacing a NOx sensor (the new sensor may have different calibration characteristics), after replacing the SCR catalytic converter, after DEF system repairs that affect injection quantity or quality, after ECU replacement or reprogramming, and when NOx-related DTCs persist after physical repairs have been completed. Common DTCs that require a NOx reset include P229F (NOx Exceeds Limit), P20EE (SCR NOx Catalyst Efficiency Below Threshold), P2201-P2204 (NOx Sensor Circuit codes), and P2BAA-P2BAF (SCR system performance codes). On the YOUCANIC UCAN-II scanner, the NOx Reset function zeroes out the stored adaptation values for DEF injection rate, resets the SCR catalyst efficiency counter, clears the NOx sensor learned offset values, and resets any inducement timers (power reduction countdowns triggered by emissions non-compliance). After performing the reset, the ECU requires several drive cycles to relearn the new component characteristics — monitor NOx sensor readings and SCR efficiency through the scanner’s live data to verify the system is functioning within parameters.