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 status

Needs verification

Not yet verified against SAE J2012_202509 / J2012DA. Treat unverified rows as a lookup aid, not repair authority.

System: Computer
Scope: iso-sae-controlled-p0
Standard: SAE J2012 / ISO 15031-6
Source: legacy-import

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.

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 fault area. They may share the same verification status as the source database.