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DTC code page

P0671: Cylinder 1 Glow Plug Circuit/Open

Quick answer: The ECU detected an open or fault in the cylinder 1 glow plug circuit.

Drivers also search this fault as cylinder 1 glow plug circuit, glow plug 1 open, cylinder 1 preheat fault.

Severity: medium Family: powertrain Related paths: 10
Meaning

What P0671 usually means

P0671 is a cylinder-specific diesel preheat code. It tells you cylinder 1 is not getting normal glow plug current or feedback during the preheat event. One dead plug may not always cause a total no-start, but it can make the engine crank longer, miss briefly after firing, and haze extra smoke from a cold start. The colder the weather and the fewer healthy plugs left in the engine, the more noticeable P0671 becomes.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Check the cylinder 1 plug resistance against the other cylinders rather than judging it in isolation.
  • Inspect the connector boot and terminal fit for heat damage or corrosion.
  • Confirm the engine complaint is worst on cold starts, not equally bad hot and cold.
Driving risk

Can you keep driving?

P0671 often allows continued driving once the engine is warm, but cold starts can worsen quickly in low temperatures. Plan repair before one failed plug becomes several.

Moderate urgency: This code often allows short-term driving, but the right fix usually comes faster when you diagnose it early instead of waiting for more codes.
Symptoms

Common symptoms

Likely causes

Common causes behind this code

  • Failed cylinder 1 glow plug
  • Open circuit in the cylinder 1 glow plug feed
  • Loose or corroded connector at the plug
  • High resistance in the harness or bus bar
  • Fault in the controller output channel for cylinder 1

Cause phrases often tied to this code: open glow plug, plug harness fault, poor terminal tension, corroded connector, controller channel fault.

Diagnostic order

Suggested workflow

  1. Verify P0671 and identify the correct cylinder layout for the engine.
  2. Measure resistance of the cylinder 1 glow plug and compare it with the rest of the bank.
  3. Check for power delivery to the cylinder 1 circuit during the preheat phase.
  4. Inspect the harness and connector for opens, corrosion, or poor contact.
  5. Replace the failed plug or repair the circuit, then recheck cold-start quality.
Avoid guesswork

Common mistakes

  • Replacing injectors because the engine shakes for a few seconds only on cold start.
  • Assuming the new plug is good without checking connector tension and power delivery.
  • Ignoring the rest of the glow plug set when several plugs are equally aged.
Repair path

Practical fix guidance

  • Repair the open circuit or replace the failed cylinder 1 glow plug as testing proves necessary.
  • Clean and secure the connector so the new plug is not starved by the same high-resistance connection.
  • Verify the next cold start is smoother and shorter before closing the job.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P0671

Useful when the driver knows the wording but not the exact DTC yet.

  • cylinder 1 glow plug circuit
  • glow plug 1 open
  • cylinder 1 preheat fault
Related search intent

Queries this page can answer naturally

  • P0671 code meaning
  • what does P0671 mean
  • cylinder 1 glow plug symptoms
  • glow plug 1 open circuit
FAQ

Quick questions about P0671

Can one glow plug really make the engine shake on cold start?

Yes. One dead cylinder during the first few seconds can create a noticeable rough idle until heat builds.

Does P0671 mean cylinder 1 has a fuel injector problem?

Not by itself. This code is specifically about the glow plug circuit for cylinder 1.

Should I replace only the failed plug?

Test the whole set first. One failed plug may be the first visible sign that the others are aging too.