P0791: Intermediate-speed circuit A must not be confused with its plausibility checks

P0791 is the intermediate-shaft speed A open-or-ground circuit result in Ford's conventional transmission tables. The summary states that the described eight-speed units have one intermediate sensor, while the ten-speed design has two. Identifying the architecture is therefore necessary before interpreting the letter A as a physical sensor location.

Electrical checks can precede motion

The cited eight- and ten-speed sensor systems support electrical fault detection without vehicle movement, with a typical maturation of approximately 1.5 seconds. A zero intermediate-speed value while stationary does not reproduce or refute that electrical result by itself.

Ford separately classifies short-to-power, intermittency, noise, dropout and plausibility. The latter comparisons use other speed information and commanded gear. Their dynamic speed thresholds should not be applied as if they were the open-or-ground criterion for P0791_14.

Keep the full architecture and failure suffix

In the TR9070 table, the related P0791 family is associated with the odd-clutch shaft speed input. That is a specific documented role, not a universal interpretation of intermediate sensor A on every gearbox.

A useful record preserves the transmission identity, full code and circuit status together with relevant speed traces. Agreement among speeds after an event cannot isolate a previously interrupted circuit. The source supplies no universal connector or sensor replacement decision; the matching electrical procedure must establish which path produced the controller's classification.

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 149. Ford PDF, page 155. Ford PDF, page 164.