OBD-II code · Powertrain (generic, extended)
P23B9 NOx Sensor Heater Sense Circuit High Bank 1 Sensor 3
Same as P23B4 with the sense voltage above the plausible range. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
Is it safe to drive with P23B9?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelySense line shorted to supply
- 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
- 1–2 h
- Emissions test
- Likely to fail
- Parts involved
- Nox Sensor B1s3 Heater
Related codes
- P23B6NOx Sensor Supply Voltage Circuit Bank 1 Sensor 3
- P23B7NOx Sensor Heater Control Circuit Range or Performance Bank 1 Sensor 3
- P23B8NOx Sensor Heater Sense Circuit Low Bank 1 Sensor 3
- P23BANOx Sensor Heater Sense Circuit Intermittent Bank 1 Sensor 3
- P23BBNOx Sensor Heater Resistance Bank 1 Sensor 3
- P23BCNOx Sensor Calibration Memory Bank 1 Sensor 3
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.