Powertrain, generic · Computer and auxiliary outputs

P068D Cylinder 7 Glow Plug Control Circuit High

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. P068D means the circuit to the cylinder 7 glow plug is shorted to battery voltage, so the driver cannot switch it off. GM's engine-module drivers detect an impedance to the supply below 0.5 Ω (0.14 Ω for low-resistance plugs) in 10 of 20 samples, lamps after two trips; Ford's 2023 Power Stroke sees 0 A in its measuring path while the plug is commanded on. A permanently powered plug can overheat and burn through.

Likely causes

Cylinder 7 plug wire touching battery positive (chafing in the harness)
Moisture or corrosion in the module or plug connector
Driver in the glow or engine module shorted (permanently on)
Glow module software (GM bulletins)

Symptoms

  • Check engine and glow plug lamp
  • Plug permanently powered, possible battery drain
  • Plug burns through, then an open-circuit code

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–600
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

P068CP0677P06BFP06CBP0670P064C

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