What it means
The factory calibration memory of the NOx sensor on bank 1 sensor 2 cannot be read or contains a checksum error. Each NOx sensor ships with a unique calibration table programmed at the factory.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The NOx sensor at bank 1, sensor 2 measures nitrogen oxides in the exhaust, and its unique calibration memory lets the emissions system interpret the reading. P225B sets when the module cannot read the calibration data from this downstream sensor or detects a checksum error.
Common causes
Most likely first.
- Sensor calibration memory corrupt
- Module software outdated, reflash may resolve
- Supply voltage outside specification
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)
How to diagnose it
- Save freeze-frame and NOx-system data and note any DEF warnings or countdown status before clearing the code.
- Inspect the bank 1 sensor 2 connector and harness for damage, corrosion, poor pin contact, or exhaust heat exposure.
- Check the sensor's power and ground supply under the specified conditions against the manufacturer's specification.
- Follow the approved diagnostic procedure to determine whether a control-module software update applies to this sensor-memory fault.
- If wiring, supply, and software are satisfactory, test the bank 1 sensor 2 assembly for an internal calibration-memory failure.
Common fixes
- Repair poor power, ground, or connector contact at bank 1 sensor 2.
- Repair damaged sensor wiring exposed to heat or corrosion.
- Apply an applicable module software update if service information confirms one.
- Replace bank 1 sensor 2 if its calibration memory remains unreadable after circuit checks.
Can I keep driving?
Driving may be possible at first, but emissions warnings, inspection failure, or a no-start countdown may follow on vehicles that enforce NOx system faults. Treat any countdown or DEF warning as urgent and arrange diagnosis.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.