Powertrain, generic · Computer and auxiliary outputs

P0679 Cylinder 9 Glow Plug Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Modern diesel glow systems switch each glow plug through its own power semiconductor (in a glow plug module or the engine module), so current and faults can be measured per plug. CARB requires glow plugs to be checked for current and voltage drop and, since model year 2010, a single faulty plug to be detected and named. P0679 means the load circuit of the cylinder 9 glow plug is open while glowing. No manufacturer document available to us uses this code – the only diesel with more than eight cylinders sold under OBD II in the US, VW's Touareg V10 TDI (2006–07), is documented only with a general glow plug tip naming no codes. The description therefore follows cylinders 1–8 (GM 200 kΩ, Ford below 1 A). A weak battery strains the glow system on such engines.

Likely causes

Glow plug cylinder 9 burnt out (element open)
Plug connector loose or corroded, terminal nut loose, wire broken
Glow module supply or ground (several cylinder codes at once)
Glow module or driver faulty, or software (GM bulletins)

Symptoms

  • Check engine light (GM also glow plug lamp)
  • Harder cold start in low temperatures
  • Rough idle and white smoke after a cold start
  • Often no symptoms when warm

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–500
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

glow plugglow plug wiringglow plug control module

Related codes

P069AP069BP06C1P06CDP0670P06F5

References: law.cornell.edu, static.nhtsa.gov, fordservicecontent.com, gsi.ext.gm.com.