P23B4
NOx Sensor Heater Sense Circuit Bank 1 Sensor 3
A general circuit fault on the heater sense feedback for the bank 1 sensor 3 NOx sensor - the line over which the ECU verifies that the heater is actually drawing current.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
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)
Common causes
Ordered by how often each turns out to be the cause.
- Open in heater sense lineCommon
Parts involved
- NOX Sensor B1s3 Heater
P23B4 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.