What it means
The NOx sensor circuit for Bank 1 Sensor 3 has a signal above 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; its signal helps the control module monitor NOx at that point in the exhaust. This code sets when the signal is higher than the expected range, which can happen if the signal wire is shorted to a supply or pinched against a B+ source.
Common causes
Most likely first.
- Signal shorted to supply
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check engine light
- Possible NOx or aftertreatment warning
- Increased NOx emissions or failed emissions test
How to diagnose it
- Use a scan tool to review freeze-frame data and live Bank 1 Sensor 3 readings to confirm the high signal and its operating conditions.
- Inspect the Sensor 3 harness for pinching, melted insulation, or contact with a battery-positive supply wire.
- Check the connector for corrosion, displaced pins, and signs that terminals are bridged or contacting a supply.
- Following the vehicle wiring diagram, test the signal circuit for a short to supply and verify connector and harness continuity.
- If the circuit tests correctly, evaluate the Sensor 3 NOx sensor and its control electronics using the manufacturer's procedure.
Common fixes
- Reposition and secure a pinched Sensor 3 harness away from supply wiring and hot surfaces.
- Repair insulation damage or a signal wire short to supply.
- Clean or replace damaged connector terminals to restore proper contact.
- Replace the Bank 1 Sensor 3 NOx sensor or control unit if testing confirms an internal fault.
Can I keep driving?
If the vehicle runs normally, drive only as needed and have the high signal diagnosed soon. The aftertreatment system may not control NOx emissions correctly, and an emissions warning or test failure may follow.
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.