Code Definition

P1873 — Oxygen sensor bank 2 sensor 2 crosscounts

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: GM

About P1873

P1873 is a manufacturer-specific powertrain diagnostic trouble code recorded for GM vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1873 is stored, the module has detected a bank-specific fault, meaning it applies only to one cylinder bank of a multi-bank engine; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1873 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

This code relates to the rear oxygen sensor on bank 2, the sensor downstream of the catalytic converter, which the Engine Control Module uses mainly to monitor catalyst efficiency rather than to control fuel directly. DTC P1873 sets when the ECM counts an insufficient number of voltage crosscounts, that is transitions of the sensor signal between rich and lean, from Bank 2 Sensor 2 over a calibrated period. A healthy post catalyst sensor still shows some activity, so very low crosscount activity suggests a lazy or biased sensor, a wiring problem, an exhaust leak drawing in air, or an exhaust c...

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