P225B

Code

Generic P — Powertrain

NOx Sensor Calibration Memory Bank 1 Sensor 2

Brand: Generic

Type: P — Powertrain

Views: UK: 25 EN: 161 RU: 53

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Read freeze frame and full trouble code list with a capable scan tool (capture live NOx sensor data and heater status)
Visual inspection of sensor wiring, connectors and harness for damage, corrosion, or pinback
Check for other related codes (heater circuit, other NOx sensors, DPF or EGR faults)
Inspect exhaust upstream/downstream for leaks and repair if found
Confirm correct sensor part number and location (not swapped)
Verify ECM software/ calibration level and technical service bulletins

Sensor heater supply voltage (when active): typically ~11–14 V (varies by vehicle)
Heater resistance (cold): typically low ohms — manufacturer-specific (commonly ~1–30 Ω); consult OEM spec
NOx sensor signal: reported as ppm or 0–5 V/CAN data depending on design; low at clean exhaust, increases with NOx concentration
Sensor operating temperature: sensor must reach target temperature to be active (often several hundred °C); heater should bring sensor to operative range
Expected behavior: Bank 1 Sensor 2 signal should be consistent and calibrated relative to Bank 1 Sensor 1 under the same conditions

Verify the code is current. Clear codes and perform a drive cycle to see if P225B returns.
Capture live data: record NOx readings for Bank 1 Sensor 1 and Bank 1 Sensor 2, heater status/voltage, and related sensor data during idle and under load.
Visually inspect connector and wiring for corrosion, damage, or poor contact. Wiggle harness while observing live data for intermittency.
Measure heater circuit: backprobe connector for supply voltage and ground while the heater is commanded ON. Compare to manufacturer spec.
Measure heater resistance (with sensor disconnected) and compare to OEM specification; replace if open or out of range.
Compare sensor output behavior: at idle and during a NOx event (e.g., during regen) the downstream sensor should respond predictably and be consistent with upstream sensor trends.
Check for exhaust leaks, soot accumulation, or contamination sources (oil/coolant leaks) and repair as needed.
If wiring, heater, and contamination are OK, check for ECM software updates or calibration relearn procedures and perform any required ECM reprogramming or sensor calibration routine per OEM service information.
If possible, swap the suspect sensor with a known-good sensor of the same type (or replace with a new sensor) to confirm whether the sensor itself is the cause.
After repairs or replacement, clear codes, run required relearn/calibration procedures, and verify proper operation through a full test drive and re-scan.