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. P06C5 reports this for cylinder 1. VW's 2.0 TDI (Jetta, Golf, Passat 2011–13) checks the type 2 s after ignition on – starting during that time caused false codes from the voltage dip, fixed with new glow module software.
Low severity. Can I keep driving?You can keep driving, although cold starts will be harder. Avoid cranking the starter repeatedly on cold days.
Cylinder 1 is numbered according to the manufacturer: check your engine's manual before working on it.
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
Most likely causes
- Wrong glow plug type fitted in cylinder 1 (steel/ceramic, voltage rating)
- Plug resistance drifted (ageing, damage)
- Glow module software or check during cranking (false report)
- Contact resistance at the plug connector
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P06C5 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 6: Control modules and outputs
- C5: Specific fault in that system
Frequently asked questions
Can I keep driving with code P06C5?
You can keep driving, although cold starts will be harder. Avoid cranking the starter repeatedly on cold days.
What causes code P06C5?
The most common causes are: wrong glow plug type fitted in cylinder 1 (steel/ceramic, voltage rating); plug resistance drifted (ageing, damage); glow module software or check during cranking (false report).
Related codes
- P06B9Cylinder 1 Glow Plug Circuit Range/Performance
- P0671Cylinder 1 Glow Plug Circuit/Open
- P066ACylinder 1 Glow Plug Control Circuit Low
- P066BCylinder 1 Glow Plug Control Circuit High
- P0670Glow Plug Control Module 1 Control Circuit/Open
Sources
- law.cornell.edu: 13 CCR 1968.2
- gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
- gsi.ext.gm.com: 25OBDG04A
- gsi.ext.gm.com: 25OBDG04B
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.