OBD-II code · Powertrain (generic, extended)
P22A9 NOx Sensor Heater Sense Circuit High (Bank 1 Sensor 2)
NOx Sensor Heater Sense Circuit High (Bank 1 Sensor 2): the signal voltage is above 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 P22A9?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyOpen signal line
- Less likelyConnector pins corroded - high contact resistance
- Less likelySupply wire pinched against B+ source
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
- 0.5–3 h
- Emissions test
- Likely to fail
- Parts involved
- Nox Sensor
Related codes
- P2224NOx Sensor Heater Sense Circuit High (Bank 2)
- P22A6NOx Sensor Heater Sense Circuit (Bank 1 Sensor 2)
- P22A7NOx Sensor Heater Sense Circuit Range/Performance (Bank 1 Sensor 2)
- P22A8NOx Sensor Heater Sense Circuit Low (Bank 1 Sensor 2)
- P22AANOx Sensor Heater Sense Circuit Intermittent (Bank 1 Sensor 2)
- P22ABO2 Sensor Positive Current Control Circuit/Open (Bank 1 Sensor 2)
- P22ACO2 Sensor Positive Current Control Circuit Low (Bank 1 Sensor 2)
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.