P0727: A missing engine-speed signal must be implausible for the transmission state

P0727 describes an engine-speed input with no signal. The cited GM transmission-controller monitor does not treat every low engine-speed value as a failure. It checks whether that value is implausible in the current operating state, and separately recognizes an unrealistically large change.

Low speed needs independent evidence that motion is expected

The documented low-value branch requires engine speed below 60 rpm for at least four seconds while turbine speed is at least 400 rpm. Ignition must be in run, the key must not be cycling and the vehicle must not be coasting with the engine intentionally off.

Those conditions distinguish a suspicious near-zero input from a legitimate stopped-engine state. An engine-speed reading taken during shutdown cannot be judged by the same comparison merely because it is low.

Pending evidence is not identical to a completed fault

Another branch marks a fault pending when the reported engine-speed change is at least 1,140 rpm. The table's wording distinguishes that pending event from the timed low-value branch, so one abrupt change should not be described automatically as a completed four-second no-signal failure.

Retain engine speed, turbine speed, key state and engine-off-coasting status together. The task runs at a 20-millisecond frequency with two-trip reporting, but the code alone does not locate a failed sensor or wire. The applicable speed-input architecture and diagnostic procedure are needed to resolve the electrical source of the implausible information.

Source and applicability

2025 GM 06B documented monitor only. Vehicle, engine and controller calibration applicability must be established separately; no model fitment is inferred from the file. GM PDF, physical page 746.