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

Symptoms of P0679

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 P0679

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

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 pin down the fault area.