P0679 Cylinder 9 Glow Plug Circuit

P0679 indicates a cylinder 9 glow plug circuit problem. The cylinder 9 glow plug path has an abnormal electrical load or circuit continuity fault.

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 assume cylinder 9 numbering from layout guesses; verify cylinder identification from service information before testing.

Useful checks before replacing parts

Check cylinder 9 glow plug resistance, control module output, command voltage, current draw, battery voltage, and cold-start freeze-frame data.
Inspect cylinder 9 wiring, connector fit, terminal corrosion, harness heat damage, module connector pins, and possible opens or shorts.
Compare cylinder 9 current and resistance with other cylinders on the same engine family to verify the faulty branch.

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.