What it means
The NOx sensor circuit for Bank 1 Sensor 3 has a signal below the expected range.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 3 is a NOx sensor in the exhaust aftertreatment system, and the control module monitors its signal to assess NOx at that exhaust location. This code sets when that signal falls below the expected range, pointing first to a signal short to ground, poor connector contact, or chafed wiring.
Common causes
Most likely first.
- Signal shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine light
- Possible NOx or aftertreatment warning
- Increased NOx emissions or failed emissions test
How to diagnose it
- Read freeze-frame data and live NOx readings for Bank 1 Sensor 3 to confirm when the low signal occurs and whether it stays low.
- Inspect the Sensor 3 harness along its route for insulation rubbed through to ground, especially near hot or moving parts.
- Check the sensor connector for corrosion, pushed-back pins, moisture, or weak terminal contact.
- Use the wiring diagram and manufacturer's test procedure to check the Sensor 3 signal circuit for a short to ground and continuity.
- If the wiring and connector pass, test the NOx sensor and its control electronics as specified for the vehicle.
Common fixes
- Repair chafed Sensor 3 wiring and protect it from the point of contact.
- Clean or repair corroded or loose connector terminals.
- Repair a signal wire shorted to ground.
- Replace the Bank 1 Sensor 3 NOx sensor or its control unit only if testing identifies an internal fault.
Can I keep driving?
If the engine runs normally, limit driving to necessary short trips and get the low signal checked soon. NOx emissions may rise, and an aftertreatment warning or failed emissions test can result.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.