OBD-II code · Powertrain (generic, extended)
P22A4 NOx Sensor Heater Control Circuit Low (Bank 1 Sensor 2)
NOx Sensor Heater Control Circuit Low (Bank 1 Sensor 2): the control-circuit voltage is below the expected range. The NOx sensor heater brings the sensor to operating temperature; a fault delays accurate NOx readings used for SCR control.
Is it safe to drive with P22A4?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyShort to ground
- Less likelyConnector pins corroded - high contact resistance
- Less likelyHarness chafing through insulation
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)
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 1–3 h
- Emissions test
- Likely to fail
- Parts involved
- Nox Sensor
Related codes
- P2219NOx Sensor Heater Control Circuit Low (Bank 2)
- P22A1NOx Sensor Circuit High (Bank 1 Sensor 2)
- P22A2NOx Sensor Circuit Intermittent (Bank 1 Sensor 2)
- P22A3NOx Sensor Heater Control Circuit/Open (Bank 1 Sensor 2)
- P22A5NOx Sensor Heater Control Circuit High (Bank 1 Sensor 2)
- P22A6NOx Sensor Heater Sense Circuit (Bank 1 Sensor 2)
- P22A7NOx Sensor Heater Sense Circuit Range/Performance (Bank 1 Sensor 2)
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.