P2221: NOx Sensor Heater Sense Circuit (Bank 2)

What it means

NOx Sensor Heater Sense Circuit (Bank 2): an electrical fault is present in the circuit. The NOx sensor heater brings the sensor to operating temperature; a fault delays accurate NOx readings used for SCR control.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The bank 2 NOx sensor heater has a sense circuit that lets the control module monitor heater operation separately from its control command. This code sets when that sense circuit has an electrical fault, so the module cannot reliably confirm heater behavior and may not get timely NOx readings.

Common causes

Most likely first.

1. Fault in the NOx sensor heater sense wiring
2. Poor or corroded connector
3. NOx sensor heater or internal sensor fault
4. Fault in the heater control circuit

Symptoms

• Check engine light or NOx warning on
• AdBlue/DEF level or quality warning
• Possible no-start countdown after ignore period
• Failed emissions inspection (NOx)

How to diagnose it

1. Review freeze-frame data and live heater status to see when the bank 2 NOx sensor sense-circuit fault occurs.
2. Inspect the bank 2 sensor connector and sense-circuit wiring for corrosion, loose pins, heat damage, or chafing.
3. Check the sense wire and its connections for opens, shorts, or excessive resistance using the manufacturer's circuit information.
4. If the sense wiring passes, test the bank 2 sensor heater and internal sense circuit according to the manufacturer's procedure.
5. If the sensor and wiring pass, check the heater control circuit for a fault affecting the sense signal.

Common fixes

• Repair an open, short, or damaged connection in the bank 2 heater sense wiring.
• Clean or repair corroded or loose terminals at the bank 2 NOx sensor connector.
• Replace the bank 2 NOx sensor if its heater or internal sense circuit fails the specified test.
• Repair the heater control circuit if it fails the specified test.

Can I keep driving?

A short drive may be possible if the vehicle runs normally, but arrange diagnosis soon and avoid ignoring a DEF or NOx warning. Faulty heater feedback can delay reliable emissions readings and may lead to a no-start countdown on vehicles that use one.