Diagnostic article Generic OBD-II
P22B6: NOx sensor 2 oxygen signal below its reporting floor
P22B6 checks the oxygen concentration signal associated with NOx sensor 2 for a below-range value.
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Documented application
2025 GM 25OBDG04B diagnostic parameter file; the cited monitor is documented, but individual vehicle, engine and calibration applicability has not been established.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
The generic name for P22B6 refers to an oxygen-sensor pumping-current trim circuit. In the cited GM implementation, the actual decision checks the oxygen concentration signal associated with NOx sensor 2. The failure threshold is below −6.00%, not a published pump-current or harness-voltage limit.
What the negative threshold means
This is a signal-validity boundary. It should not be read as a physically meaningful negative oxygen content or a target for normal exhaust. The controller checks for 100 failures out of 200 samples at a 25 ms task rate. The row is Type B with two-trip reporting.
Engine operation, system voltage above 11 V, a fully operative sensor and an enabled combustion mode qualify the test. An invalid NOx sensor 2 condition prevents it from being accepted.
A useful diagnostic approach
Verify which scan parameter is being displayed: the raw or processed oxygen signal and the NOx concentration are different measurements from this sensor system. A low NOx ppm value does not satisfy the oxygen-percent failure criterion. Also check readiness before treating an absent code as a passing measurement-range test. The summary does not provide a pin-voltage conversion or a procedure for adjusting pump current; applying a generic oxygen-sensor voltage test could therefore answer the wrong diagnostic question.
Source and application limits
This explanation covers the cited 2025 GM monitor. Confirm the vehicle and calibration in its service information before applying these limits; inclusion in this file does not establish model compatibility. GM diagnostic parameters, PDF page 1437.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
O2 Sensor Pumping Current Trim Circuit Low Bank 1 Sensor 2
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT