P220B
NOx Sensor Supply Voltage Circuit (Bank 1 Sensor 2)
The supply voltage rail to the NOx sensor on bank 1 sensor 2 is faulty — typically a fuse, harness break, or short. NOx sensors need a clean stable supply for the heater and the wide-band measurement cell.
- 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.
- Supply rail faultCommon
Parts involved
- NOX Sensor
P220B 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.