NOx Aftertreatment Monitor Not Ready

NOx Aftertreatment Monitor Not Ready — What it means

If you encounter the message “NOx Aftertreatment Monitor Not Ready” on your vehicle’s scan tool, it indicates that the NOx (nitrogen oxides) aftertreatment system is not yet prepared to monitor and control emissions effectively. This issue can arise during emissions testing or vehicle inspections, and it’s crucial to address it to ensure your vehicle meets environmental standards. Here are steps to take if you come across this message:

Understand how the NOx Aftertreatment System: Before addressing the issue, it’s essential to have a basic understanding of the NOx aftertreatment system. This system is designed to reduce nitrogen oxide emissions from the vehicle, contributing to cleaner air and compliance with environmental regulations.

Diesel vehicles are now required to reduce NOx even further. A special catalytic converter is used to accomplish the NOx reductions. The catalytic converter is treated with a special washcoat containing zeolites. The zeolite acts as a molecular “sponge” to trap the NO and NO2 molecules in the exhaust stream.

In some implementations, injection of a reactant before the aftertreatment purges it. NO2 in particular is unstable, and will join with hydrocarbons to produce H2O and N2.

NOx sensor

The system monitors the function of the NOx aftertreatment to ensure that tailpipe emissions remain within acceptable limits. It is only used in diesel vehicles.

It’s a “Two-Trip” Monitor. If a fault is found on the first trip, the computer temporarily saves the fault in its memory as a Pending Code. The computer does not command the MIL on at this time. If the fault is sensed again on the second trip, the computer commands the MIL “On,” and saves the code in its long-term memory.

What to do next if you see the message

Reset the MIL (Malfunction Indicator Lamp):
After completing the necessary drive cycles and addressing any faults, reset the Malfunction Indicator Lamp (check engine light) using the scan tool. This step is vital to clear any existing codes and allow the NOx aftertreatment monitor to start its monitoring process anew.

Re-test the System:
Once you’ve followed the recommended procedures, take your vehicle for emissions testing or inspection again. Use the scan tool to check the readiness status of the NOx aftertreatment monitor. If the system is now ready, you should pass the test without any issues.

Addressing the “NOx Aftertreatment Monitor Not Ready” message requires a systematic approach, involving proper driving cycles, fault code checks, and, if necessary, repairs. Following these steps will help ensure that your vehicle meets emissions standards and contributes to a cleaner environment.

©, 2022 Rick Muscoplat