P0671: Cylinder 1 Glow Plug Circuit/Open
What to do
Driveable, and quite possibly unnoticeable until cold weather — one failed plug out of four rarely shows in summer. Expect a suggestion to replace all of them together: the labour is most of the cost, they are all the same age, and a seized plug that snaps during removal is an expensive complication. That advice is usually genuine rather than an upsell.
What this code means
A circuit fault on cylinder 1's glow plug. Because the control module monitors each plug's current individually, it can name the specific cylinder — which is genuinely useful, since glow plugs fail one at a time and a single failed plug is often unnoticeable until the weather turns.
The practical trap is removal rather than diagnosis. Glow plugs seize in the cylinder head with age and carbon, and a plug that snaps off during removal turns a modest job into a specialist extraction, sometimes with the head removed. That risk is why many workshops advise replacing all of them once one has failed: the labour dominates the parts cost, and the others are the same age.
A plug that has already been electrically dead for a long time is the most likely to seize, which is an argument for attending to this promptly rather than waiting for winter.
Likely causes
Start here
- Failed glow plug · moderate
- Corroded or loose connector · easy
- Broken glow plug supply wire · moderate
Less common
- Failed glow plug control module · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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.
- What actually fixed it — or that nothing did, which is worth knowing too.
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