What it means
The factory calibration memory of the NOx sensor on bank 1 sensor 1 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 1 measures nitrogen oxides in the exhaust, and its calibration memory holds data the emissions control system needs to interpret that measurement. P225A sets when the module cannot read that calibration data or detects a checksum error for this specific sensor.
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- Module software outdated, reflash may resolve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
- Record freeze-frame and NOx-system data, including any DEF or countdown warnings, before clearing codes.
- Check the bank 1 sensor 1 connector, harness, power, and ground for damage or poor connections that could disrupt memory access.
- Measure the sensor supply voltage under the specified conditions and compare it with the manufacturer's specification.
- Use the vehicle's approved diagnostic procedure to check for applicable control-module software updates or calibration-memory faults.
- If supply, wiring, and software checks pass, test or replace the bank 1 sensor 1 assembly according to service information.
Common fixes
- Repair damaged wiring or poor power and ground connections to bank 1 sensor 1.
- Correct a supply voltage problem affecting the sensor.
- Update the relevant module software if an applicable update is confirmed.
- Replace bank 1 sensor 1 if its calibration memory cannot be read after circuit checks.
Can I keep driving?
The vehicle may remain drivable initially, but NOx warnings, emissions failure, or a later no-start countdown can occur depending on the vehicle. Do not ignore a countdown or DEF warning; arrange diagnosis promptly.
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.