P0731: First-gear ratio checks require a stable commanded gear

P0731 identifies a problem with the expected first-gear relationship in Ford's general transmission monitor. The controller does not simply compare two speed numbers at any moment. Its evaluation depends on a commanded gear and an operating window in which that comparison is meaningful.

A launch transient is not automatically a failed ratio test

The example entry conditions include positive torque, a minimum throttle opening, adequate input and output speeds, and more than half a second without shifting. Forward range must also have been selected long enough. A speed relationship captured during the transition into first gear may therefore fall outside the documented check.

Ford's forward-ratio criterion requires an error above 30 rpm lasting more than 2.5 seconds and six occurrences across key cycles, without solenoid faults being detected. The repeated-event logic matters when a single apparently normal first-gear event is used to claim the problem is gone.

Identify the architecture before naming a failed part

In the TR9070 table, P0731 is listed as unknown first-gear state; P073F identifies failure to engage first and P072C failure to disengage it. Preserve that distinction if the code came from this architecture.

Useful evidence includes commanded gear, shift completion, input/output speeds and the status of relevant electrical diagnostics. A ratio conclusion is only as reliable as those inputs. The summary does not map P0731 to one universal clutch or repair; verification must follow the specific transmission's measured behavior.

Source and applicability

Ford 2024–2025 gasoline OBD operation summary, July 16 2024 revision; only the cited monitor and transmission architectures. No individual vehicle fitment or universal calibration is inferred. Ford PDF, page 152. Ford PDF, page 153. Ford PDF, page 167.