P079C: Clutch three uses a lower slip threshold than C1 and C2

P079C identifies excessive slip of clutch three in the cited GM hybrid transmission. C3 is not evaluated with the same slip and torque thresholds used for the first two clutches, so a generic description of “transmission slipping” loses useful diagnostic detail.

The C3 combination

The failure row specifies C3 slip above 100rpm for 0.625 seconds. Commanded pressure must be at least 1800kPa, estimated torque at least 20Nm and fill detected. The lower torque requirement is significant when assessing whether a recorded event could satisfy this particular monitor.

Passing behavior requires C3 slip below 20rpm for 0.125 seconds while the listed command, torque and fill conditions remain satisfied. A drop below the failure threshold alone is therefore not necessarily the same as reaching the pass threshold.

Capture the relevant clutch state

A useful diagnostic record contains C3 slip, its own pressure command, torque estimate and fill flag together. C1 or C2 data cannot establish the C3 relationship, and a pressure request must not be described as a measured hydraulic pressure.

The code indicates inadequate synchronization under the documented commanded state; the table does not identify why it happened. It provides no clutch replacement decision, fluid-pressure test connection or adaptation procedure. Those depend on the actual transmission and service information. Hybrid-transmission diagnosis should be performed by a trained technician with appropriate torque-control and high-voltage precautions.

Source and applicability

GM 2010 10OBDG10 Hybrid Diagnostics, only the cited controller and monitor. These are historical calibration examples; individual vehicle, engine and hardware applicability is not established. GM PDF, page 197.