P0871: system-pressure sensor checked against clutch pressure

P0871 is a system-pressure-sensor consistency diagnostic in this transmission. It runs within a pressure-recovery routine triggered by a system or component fault, rather than being an ordinary continuous comparison under every driving condition.

A controlled reference is created

The recovery routine attempts different pressure targets. If a target cannot be attained, it checks system-pressure measurement against a selected clutch-pressure sensor. The description explains that the appropriate gear is disengaged when possible and clutch pressure is increased until the clutch is completely closed; the two pressure readings should then be similar.

A difference of at least 2.5 bar at either of two open-loop system-pressure targets is listed, with 2,000 milliseconds of confirmation. The routine must be requested, its run conditions met, and a target step must have failed during that instance.

What the comparison means

A disagreement between system and clutch pressure outside the prepared state is not automatically a failed P0871 test. Conversely, an electrical-range pass from the system sensor does not prove its pressure reading agrees with the independent reference.

Verification should use the correct professional recovery/consistency procedure and establish the completed comparison result. The table describes how the controller distinguishes a sensor discrepancy from other pressure-control problems; it does not supply a safe manual actuation sequence or establish the required repair by itself.

Documentation and applicability

These details describe the monitor in GM’s 2025 25OBDG07A Part2 file. Its application-matrix filename does not match the download index, so model and engine applicability remain unresolved. Use the vehicle’s correct service information before applying these calibration details.

GM diagnostic table, PDF page 980.