OBD-II code · Powertrain (generic, extended)
P22A8 NOx Sensor Heater Sense Circuit Low (Bank 1 Sensor 2)
NOx Sensor Heater Sense Circuit Low (Bank 1 Sensor 2): the signal 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 P22A8?
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
- 0.5–3 h
- Emissions test
- Likely to fail
- Parts involved
- Nox Sensor
Related codes
- P2223NOx Sensor Heater Sense Circuit Low (Bank 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)
- P22A9NOx Sensor Heater Sense Circuit High (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)
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.