P0678: Cylinder8 open-load evidence depends on glow heating mode

P0678 is the cylinder 8 glow-plug circuit/open entry in Ford’s diesel monitor. The document explicitly identifies this channel as V8 diesel only. Its presence in a generic code list does not establish that the same cylinder or glow-system arrangement exists on every diesel engine.

The monitored current has an operating context

The check is performed with glow plugs in heating mode and specifies approximately one second for failure registration. The individual glow-plug open-load threshold is below 1 A. A zero or low reading when heating is inactive would answer a different question and cannot be judged against this criterion alone.

The threshold paragraph also covers reductant heaters, with a different current limit. Keeping those load types separate is necessary before interpreting a current trace from a shared glow/heater-control system.

A channel result still needs localization

Retain the cylinder 8 identity, requested heating state, observed or reported current and related control-module faults. The code distinguishes this channel from cylinder 7, while the documented open-load method is shared; it does not establish a different test merely because the cylinder number changes.

The source does not identify whether the interruption lies in the glow element, connection, wiring or driver. It supplies no universal bench resistance or safe direct-power procedure. The applicable V8 diagnostic information is needed to turn the channel-specific low-current evidence into a justified repair.

Source and applicability

Ford 2023–2024 diesel OBD summary, August 25, 2023 revision; only the described monitor examples. Confirm the engine and calibration before applying values. The monitor explanation does not identify a failed part or replace the applicable service procedure. Ford PDF, page 114.