What it means
The NOx sensor circuit for Bank 1 Sensor 3 has an intermittent or erratic signal.
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 aftertreatment exhaust, and the control module monitors its signal for a stable reading. This code sets when that signal cuts in and out or becomes erratic, often because a connector loses contact or the harness moves against a vibrating part.
Common causes
Most likely first.
- Intermittent contact at connector
- Connector with intermittent contact under vibration
- Harness routed against vibrating component
Symptoms
- Check engine light
- Possible NOx or aftertreatment warning
- Increased NOx emissions or failed emissions test
How to diagnose it
- Check freeze-frame records and live Bank 1 Sensor 3 data for dropouts, spikes, or changes associated with engine speed or vehicle movement.
- Inspect the Sensor 3 connector for looseness, corrosion, damaged locks, or terminals that may lose contact under vibration.
- Trace the harness and look for chafing or routing against an exhaust component or other vibrating part.
- With live data displayed, gently move the harness and connector to see whether the Sensor 3 signal changes, taking care around hot exhaust parts.
- If no wiring fault is found, test the sensor and circuit for intermittent faults using the manufacturer's procedure.
Common fixes
- Secure the Sensor 3 harness so it cannot rub against or vibrate on nearby parts.
- Repair a loose connector lock or poor terminal contact.
- Replace damaged wiring or connector terminals causing intermittent contact.
- Replace the Bank 1 Sensor 3 NOx sensor if the signal still drops out with a sound harness and connector.
Can I keep driving?
If the vehicle runs normally, short trips may be possible, but arrange diagnosis soon because the fault can recur unpredictably. NOx emissions may increase, and an aftertreatment warning or emissions-test failure may occur.
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.