P2221
NOx Sensor Heater Sense Circuit Bank 2
Emissions (NOx / SCR)
Generic OBD-II
Medium
What it means
P2221 means there's a fault in the heater-sense circuit of the bank 2 NOx sensor. The heater warms the sensor to operating temperature so it can measure nitrogen-oxide levels for the SCR/emissions system; when the ECM can't verify that circuit, the sensor's readings can't be trusted. It's usually a failing sensor heater, a wiring fault, or a poor connection, and the engine itself still runs.
Medium
Can I keep driving? Usually drivable, but the bank 2 NOx sensor can't work until heated, so emissions monitoring is affected and diesels may eventually derate; repair soon.
Common symptoms
What you'll notice
- Check-engine light on
- Higher tailpipe emissions or a failed emissions test
- SCR / emissions-system warning (diesel)
- Reduced-power derate if the fault escalates (diesel)
Common causes
Most likely first
- Faulty NOx sensor heater element (bank 2)Likely
- Heater sense wiring open, shorted, or chafedCommon
- Poor connection or corrosion at the NOx sensor connectorCommon
- Ground or reference fault on the heater sense circuitLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check for companion bank 2 NOx codes (P2220, P2222, P2223).
- Inspect the bank 2 NOx sensor connector and heater wiring for damage, corrosion, or a loose pin.
- Measure the heater sense circuit voltage and compare against spec.
- Test the sensor's heater element resistance; an open or out-of-range heater confirms the sensor.
- Replace the NOx sensor if the heater fails testing, then clear and re-run the monitor.
FAQ
Quick answers
Is it safe to drive with P2221?+
The engine runs normally, but without a working heater the bank 2 NOx sensor can't monitor emissions, and some diesels will eventually reduce power to force a repair.
Can I just clear P2221?+
It will clear, but a heater-sense fault from wiring or the sensor will set it again.
Related codes
Often seen with P2221
Read & clear P2221 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX