NOx Sensor A Circuit Low Input (Bank 1)

The NOx sensor measures the amount of nitrogen oxides in the exhaust. If it reports too low a signal, the engine thinks the emissions are lower than they really are, which can lead to increased pollution and may affect performance.

The Engine Control Module (ECM) expects the NOx sensor to produce a voltage between 0.2 and 4.5 volts during operation. A signal below 0.2 volts triggers this code.

Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.

1. 11. Inspect the NOx sensor wiring and connectors for damage or corrosion. If any issues found, repair or replace as needed. - Decision: Were any issues found? Yes: Fix issues. No: Go to step 2.
2. 22. Measure the voltage output from the NOx sensor while the engine is running. Using a multimeter, you should see a voltage between 0.2 and 4.5 volts. - Decision: Is the voltage within range? Yes: Go to step 3. No: Replace the NOx sensor and recheck codes.
3. 33. Inspect the exhaust system for any leaks prior to the NOx sensor. A leak can affect the readings of the sensor. - Decision: Are there any exhaust leaks? Yes: Repair leaks. No: Go to step 4.
4. 44. If the previous steps are clear, check the ECM for updates or issues. A faulty ECM may misread the sensor input. - Decision: Is the ECM functioning correctly? Yes: Further diagnostics may be required. No: Replace the ECM.

• Faulty NOx sensor
• Wiring issues or damaged connectors
• Faulty ECM
• Exhaust system leaks
• Contamination in the exhaust gas

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