Every smart NOx sensor carries its own control unit with a memory holding trim and reference data written for that individual probe at the factory. P23BC means this memory in sensor 3 on bank 1 cannot be read or fails its integrity check, so the engine module can no longer trust the readings. No manufacturer documents P23BC publicly. GM's 2025 table hints at what is stored there: for its sensing-element test P23C1, a reference value measured on the new sensor at the supplier plant sits in the sensor EEPROM. Ford's 2023 diesel summary files RAM, ROM and EEPROM checksum errors of the front sensor controller under P2200 instead. CARB treats NOx sensor faults as emission-relevant. P225A and P225B are sensors 1 and 2; a corrupt memory cannot be repaired.
Medium severity. Can I keep driving?You can usually keep driving in the short term, but get it repaired soon: on many diesels, the warning eventually limits starting or engine power.
Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.
Symptoms
- Check engine light on
- Sensor 3 readings ignored by the engine module
- SCR monitoring cannot complete
Most likely causes
- Memory inside the sensor control unit corrupted or failed
- Voltage dips or spikes on the sensor supply disturbing the memory
- Replacement sensor with a calibration that does not match the vehicle
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: easy
- It affects emissions.
What each character of P23BC means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 3: Ignition and misfires
- BC: Specific fault in that system
Frequently asked questions
Can I keep driving with code P23BC?
You can usually keep driving in the short term, but get it repaired soon: on many diesels, the warning eventually limits starting or engine power.
What causes code P23BC?
The most common causes are: memory inside the sensor control unit corrupted or failed; voltage dips or spikes on the sensor supply disturbing the memory; replacement sensor with a calibration that does not match the vehicle.
Related codes
- P23ABNOx Sensor Processor Performance (Bank 1 Sensor 3)
- P23C1NOx Sensor Performance - Sensing Element (Bank 1 Sensor 3)
- P225ANOx Sensor Calibration Memory (Bank 1 Sensor 1)
- P225BNOx Sensor Calibration Memory (Bank 1 Sensor 2)
Sources
- law.cornell.edu: 13 CCR 1968.2
- gsi.ext.gm.com: 25OBDG04B
- fordservicecontent.com: obd summary diesel 2023
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.