P0971: solenoid C high circuit has architecture-specific consequences

P0971 diagnoses a high-voltage signature on pressure-control solenoid C's circuit. The cited TCM interprets the voltage against a short-to-source specification below 0.5 ohm between signal and controller power.

A circuit code does not identify hydraulic pressure

The same source row covers C clutch-control assignments in several geared transmissions and line-pressure control in a CVT. The letter alone therefore cannot establish a physical valve location or the likely shift symptom. It also cannot establish excessive fluid pressure: the monitored quantity is electrical voltage.

The high-circuit failure time exceeds 0.06 second within a sample period exceeding 0.13 second. That is distinct from the longer windows shown for C open and low faults, so a brief high-input event can have a different recording history.

Verification must keep the supply active

The source requires the mapped high-side driver on, qualifying power mode and battery voltage between 9 and 32 volts for more than one second. A no-driver mapping disables the diagnostic. Confirm those conditions when interpreting an apparent post-repair pass.

Preserve the transmission assignment, supply state and any intermittent voltage evidence. Verification should demonstrate a passing high-circuit monitor and the applicable operational checks, rather than rely solely on a successful shift. The summary does not authorize external energization of the solenoid or establish a mandatory replacement; its impedance specification describes detection capability, not an energized resistance-test procedure.

Source and applicability

Documented monitors in gm-2025-03a, model year 2025. These are module/calibration examples; vehicle, engine and transmission applicability must be confirmed independently. GM 2025-03a, page 1153.