P074E: Sixth-gear engagement failure is distinct from being stuck in sixth

P074E means sixth gear could not be engaged. That direction of the transition matters: it is different from a transmission already in sixth that cannot disengage. The GM monitor follows the active attempt to enter the gear.

Differential speed and timeout are alternatives

The table compares synchronizer differential speed with an initial gear limit plus 250 rpm and with a separate state-dependent maximum. It also evaluates unmet actuation-state transition conditions combined with a calibrated timeout.

The sixth-gear request must be present and actuation active, system pressure must exceed 4.5 bar, and the application must not be in error or bypass state. At least four failed engagement attempts are required for confirmation.

Match the complaint to the recorded sequence

Preserve the requested gear, speed difference and failed actuation state. A complaint about being stuck in sixth does not independently confirm the engagement failure described by P074E; the command history distinguishes those events.

The same broad strategy applies to other engagement codes, but the exact sixth-gear limits remain calibration-specific. The table’s added 250 rpm is not a universal maximum speed difference. It also does not identify a damaged synchronizer, failed sensor or hydraulic component. Follow the installed transmission’s approved diagnostic procedure and referenced state limits before selecting a repair, rather than forcing additional shifts or interpreting a single unsuccessful request as complete proof.

Source and applicability

This explanation covers the cited GM monitor, not every vehicle carrying this code. The application-matrix filename does not resolve cleanly to this file, so no model or engine fitment is assigned. GM diagnostic table, PDF page 1044; GM diagnostic table, PDF page 1045.