P0670: Glow Plug Control Module 1 Control Circuit/Open
What to do
Driveable, and probably unnoticeable in warm weather. Expect hard starting, white smoke and rough running when cold. Worth fixing before winter rather than during it — a diesel that will not start on a frosty morning is a poor time to discover this.
What this code means
A fault in the circuit controlling the glow plug module. Modern diesels do not switch glow plugs with a simple relay — a dedicated module drives each plug individually, monitors its current, and continues heating after the engine has started to reduce cold-running emissions and noise.
That individual monitoring is what makes P0671 onward possible, and it is also why a fault in the module itself disables every plug at once. The distinguishing symptom is entirely seasonal: nothing in summer, then hard starting, white smoke and a rough first minute on the first cold morning.
Likely causes
Start here
- Failed glow plug control module · moderate
- Corroded or loose connector · easy
- Broken wire in control circuit · moderate
Less common
- Corroded heavy supply cable · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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