P0777: C2 release behavior behind the solenoid B stuck-on code

The reviewed P0777 monitor follows the GR10 C2 clutch as it is commanded off during a shift. If the clutch continues to carry torque, its calculated slip remains near zero. GM uses that behavior to identify a hydraulically stuck-on pressure-control solenoid B, even though its electrical circuit can still operate normally.

The shift category changes the judgment

C2 slip below 50 rpm is the listed failure condition for power downshifts and the general shift case; garage shifts use a 100-rpm boundary. The base durations are 0.60, 0.25 and 0.15 second respectively, followed by calibrated offsets. The support table also varies C2 exhaust delay with transmission-fluid temperature.

Consequently, low slip at the very beginning of a pressure-release command is not enough to reproduce the diagnostic. The control phase and allowed hydraulic exhaust time must be understood before interpreting that trace.

Inputs and verification

C2 slip is calculated from transmission shaft-speed information rather than measured by a dedicated C2 slip sensor. Relevant speed-sensor faults can therefore inhibit or undermine the comparison. GM also requires functioning driver circuits and excludes active service fast learn and solenoid-cleaning operation.

After diagnosis, verify an eligible C2 release event, including temperature and shift type, rather than relying on an electrical resistance result. The continuation associates this monitor with the GR10 C2 CB128910R clutch; that does not establish applicability to other transmissions using P0777. The source lists Type A, one-trip reporting but gives no component-replacement conclusion.

Source: GM monitor, PDF page 2084; GM monitor, PDF page 2085; GM monitor, PDF page 2086; GM monitor, PDF page 2087; GM monitor, PDF page 2089; GM monitor, PDF page 2431.