What it means
The NOx sensor heater control circuit for Bank 1 Sensor 3 is reporting a low condition. This indicates an electrical fault in that circuit; it does not mean the engine’s lambda sensor or closed-loop fuel control is inactive.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The heater control circuit supplies and controls the heater in the Bank 1 Sensor 3 NOx sensor so it can reach operating temperature. This code sets when the heater control circuit is detected low, commonly from a short to ground or excessive resistance at a connector; it does not indicate a fault with engine lambda control.
Common causes
Most likely first.
- Heater control line 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
- Review freeze-frame data and live heater status for Bank 1 Sensor 3, along with related codes, to establish when the low condition appears.
- Inspect the Sensor 3 heater harness for chafed insulation or a wire contacting ground near the exhaust.
- Check the heater connector for corrosion, moisture, loose fit, or terminals with poor contact.
- Use the wiring diagram and manufacturer's procedure to test the heater control line for a short to ground and excessive resistance.
- If the wiring and connector pass, test the Sensor 3 heater and control module for an internal fault.
Common fixes
- Repair heater wiring rubbed through and contacting ground.
- Clean or repair corroded or loose heater connector terminals.
- Repair high resistance or a short to ground in the heater control circuit.
- Replace the Bank 1 Sensor 3 NOx sensor or heater control module if testing confirms an internal fault.
Can I keep driving?
If the vehicle runs normally, keep driving to a minimum until the heater circuit is checked. The NOx sensor may not warm and report correctly, allowing emissions to rise or triggering an aftertreatment warning.
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.