Powertrain, generic · Computer and auxiliary outputs

P06CD Cylinder 9 Glow Plug Incorrect

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

A glow plug has no identification; the control unit recognises its type only from its electrical behaviour – cold resistance at switch-on and how resistance rises during heating (R = U/I). A Beru patent describes how steel and ceramic plugs are told apart this way so the right heating profile is used and a wrong or mixed type is reported. A low-voltage plug on an 11 V control burns out, an 11 V plug on a low-voltage control glows too weakly. GM uses 'incorrect' for any resistance outside the window: the 2025 diesels check 0.22–2.00 Ω (15 of 25 samples, two trips), the L5P glow module a ramp-dependent window. P06CD reports this for cylinder 9. No manufacturer document available to us uses this code for cylinders 9 and above; the description follows cylinders 1–8.

Likely causes

Wrong glow plug type fitted in cylinder 9 (steel/ceramic, voltage rating)
Plug resistance drifted (ageing, damage)
Glow module software or check during cranking (false report)
Contact resistance at the plug connector

Symptoms

  • Check engine and glow plug lamp
  • Harder cold start or white smoke
  • Possibly plug burnt out (low-voltage plug on 11 V control)
  • Code after replacing plugs

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–500
Time0.5–3 h

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

Parts involved

glow plugglow plug control module

Related codes

P06C1P0679P069AP069BP0670

References: law.cornell.edu, patents.google.com, techtips.ie.