Powertrain, generic · Computer and auxiliary outputs

P0671 Cylinder 1 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; a faulty channel is switched off. CARB requires glow plugs to be checked for correct current and voltage drop and, since model year 2010, a single plug outside specification to be detected and named. P0671 means the load circuit of the cylinder 1 glow plug is open while glowing. Thresholds: GM engine-module drivers 200 kΩ or more (two trips), GM's L5P glow module less than 4.0 A at over 6 V, Ford's 2023 Power Stroke less than 1 A for about 1 s. Older GM systems (LB7/LLY, LML) report open and short under this one code. Chrysler advises checking the main B+ feed and ground of the glow module first when several cylinder codes appear together.

Likely causes

Glow plug cylinder 1 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 3.0 L 2020)

Symptoms

  • Check engine light (GM also glow plug lamp)
  • Harder cold start in low temperatures
  • Rough idle, knocking and white or blue 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

P066AP066BP06B9P06C5P0670P052F

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