P0678 Cylinder 8 Glow Plug Circuit

P0678 points to a cylinder 8 glow plug circuit fault. The cylinder 8 glow plug circuit is open, shorted, or drawing current outside the expected range.

Code details

Generic OBD-II · P0

System: Computer
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not overlook connector or harness heat damage when cylinder-specific glow plug codes repeat after plug replacement.

Symptoms of P0678

Check-engine light, sometimes with several unrelated codes at once.
Warning lights, a no-start, or intermittent electrical faults.
Communication or module-reset problems on a scan tool.

Common causes of P0678

Low battery voltage, poor grounds, corroded connectors, or blown fuses.
Wiring or network (CAN bus) faults between modules.
A module software/programming issue, or rarely a failed controller.

Useful checks before replacing parts

Measure cylinder 8 glow plug resistance, voltage drop, command status, current draw, battery voltage, and freeze-frame temperature data.
Inspect cylinder 8 wiring, connector corrosion, terminal tension, heat damage, module output, and harness routing near exhaust components.
Test cylinder 8 during an active glow command and compare current response with cylinders that do not set codes.

Related OBD-II codes

These nearby computer entries can help compare wording and pin down the fault area.