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Home / DTC / P0671 — Cylinder 1 Glow Plug Circuit/Open

P0671 — Cylinder 1 Glow Plug Circuit/Open

Detailed page for trouble code P0671.

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Code

P0671

Generic P — Powertrain

Cylinder 1 Glow Plug Circuit/Open

Brand: Generic
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted glow plug in cylinder 1
  • Broken or corroded wiring or connector to glow plug 1
  • Failed glow plug relay or control module
  • Blown fuse for glow plug/heater circuit
  • Faulty ECM/PCM output driver (less common)
  • Poor battery or charging system voltage during test

Symptoms

  • Hard starting, especially in cold conditions
  • Longer-than-normal crank time before engine starts
  • Glow plug/engine preheat warning lamp illuminated or flashing
  • Rough idle or white smoke on cold start
  • Increased emissions or poor cold-driveability

What to check

  • Retrieve freeze frame and related codes; verify P0671 is current and not a pending/misleading code
  • Inspect battery condition and charging voltage (low voltage can cause false faults)
  • Check glow plug fuse(s) and relay(s) for continuity and operation
  • Visually inspect wiring harness and connector at cylinder 1 glow plug for corrosion, damage, or loose pins
  • Measure resistance of glow plug 1 with plug removed (compare to other cylinders and spec)
  • Check for voltage at the glow plug connector while the preheat circuit is commanded on (use a scope or DMM; some systems use PWM)

Signal parameters

  • Glow plug resistance (cold): typically ~0.3 Ω to 3 Ω depending on design — compare to manufacturer spec and other cylinders
  • Applied voltage during preheat: roughly battery voltage (~11–14 V) on older systems; modern systems may use PWM or reduced average voltage
  • Current draw per glow plug: can range from about 5 A (high-resistance plugs) to 20+ A (low-resistance plugs) — check spec
  • ECM sees open if resistance is very high or infinite, or if commanded current is below expected threshold

Diagnostic algorithm

  1. Confirm code: clear DTCs, cycle key to preheat, and re-scan to verify P0671 returns. Note related codes (other cylinder codes, P0685, battery/charging codes).
  2. Check battery and charging system: verify battery voltage >12.2 V and charging system operating; low voltage can cause false faults.
  3. Inspect: visually inspect glow plug 1 connector, wiring, and ground for corrosion, heat damage, breaks, or loose pins. Repair any physical damage.
  4. Check fuses/relay: verify glow plug fuse(s) and relay(s) are present and functioning. Replace or bench-test if suspect.
  5. Measure glow plug resistance: unplug glow plug 1 and measure ohms from tip to body. Compare to spec and other cylinders. Open or very high resistance indicates a bad plug.
  6. Apply voltage/measure current: with preheat commanded (or carefully apply bench voltage), measure voltage at the glow plug terminal and measure current draw. Low/zero voltage or abnormal current indicates wiring/driver issue.
  7. Continuity test: check continuity between ECM glow driver pin and glow plug connector; check ground continuity as well.
  8. Swap test: if safe and practical, swap glow plug 1 with another cylinder's plug. If the code moves with the plug, replace the plug. If it remains on cylinder 1, suspect wiring or ECM output.
  9. Inspect ECM/driver: if wiring, connectors, fuses, relay, and glow plug are good, inspect the ECM output and related control circuits. Replace or reprogram ECM only after confirming failures.
  10. Repair and verify: repair/replace faulty components (glow plug, wiring, connector, relay, fuse, or ECM), clear codes and perform repeated preheat/start cycles to confirm the fault is resolved.

Likely causes

  • Corroded/broken connector or wiring to glow plug 1 (most common)
  • Failed glow plug (open/high-resistance)
  • Blown fuse or bad glow relay
  • ECM driver fault (rare)
  • Low battery/voltage problem causing abnormal readings

Fault status

⚠️ Status
P0671 — Cylinder 1 Glow Plug Circuit/Open: ECM detected open or abnormally high resistance in the glow plug/heater circuit for cylinder 1 during preheat/operation.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours
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Code

P0671

LAND ROVER P — Powertrain

Cylinder 1 bright open circuit

Brand: LAND ROVER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted glow plug in cylinder 1
  • Broken or corroded wiring or connector to glow plug 1
  • Failed glow plug relay or control module
  • Blown fuse for glow plug/heater circuit
  • Faulty ECM/PCM output driver (less common)
  • Poor battery or charging system voltage during test

Symptoms

  • Hard starting, especially in cold conditions
  • Longer-than-normal crank time before engine starts
  • Glow plug/engine preheat warning lamp illuminated or flashing
  • Rough idle or white smoke on cold start
  • Increased emissions or poor cold-driveability

What to check

  • Retrieve freeze frame and related codes; verify P0671 is current and not a pending/misleading code
  • Inspect battery condition and charging voltage (low voltage can cause false faults)
  • Check glow plug fuse(s) and relay(s) for continuity and operation
  • Visually inspect wiring harness and connector at cylinder 1 glow plug for corrosion, damage, or loose pins
  • Measure resistance of glow plug 1 with plug removed (compare to other cylinders and spec)
  • Check for voltage at the glow plug connector while the preheat circuit is commanded on (use a scope or DMM; some systems use PWM)

Signal parameters

  • Glow plug resistance (cold): typically ~0.3 Ω to 3 Ω depending on design — compare to manufacturer spec and other cylinders
  • Applied voltage during preheat: roughly battery voltage (~11–14 V) on older systems; modern systems may use PWM or reduced average voltage
  • Current draw per glow plug: can range from about 5 A (high-resistance plugs) to 20+ A (low-resistance plugs) — check spec
  • ECM sees open if resistance is very high or infinite, or if commanded current is below expected threshold

Diagnostic algorithm

  1. Confirm code: clear DTCs, cycle key to preheat, and re-scan to verify P0671 returns. Note related codes (other cylinder codes, P0685, battery/charging codes).
  2. Check battery and charging system: verify battery voltage >12.2 V and charging system operating; low voltage can cause false faults.
  3. Inspect: visually inspect glow plug 1 connector, wiring, and ground for corrosion, heat damage, breaks, or loose pins. Repair any physical damage.
  4. Check fuses/relay: verify glow plug fuse(s) and relay(s) are present and functioning. Replace or bench-test if suspect.
  5. Measure glow plug resistance: unplug glow plug 1 and measure ohms from tip to body. Compare to spec and other cylinders. Open or very high resistance indicates a bad plug.
  6. Apply voltage/measure current: with preheat commanded (or carefully apply bench voltage), measure voltage at the glow plug terminal and measure current draw. Low/zero voltage or abnormal current indicates wiring/driver issue.
  7. Continuity test: check continuity between ECM glow driver pin and glow plug connector; check ground continuity as well.
  8. Swap test: if safe and practical, swap glow plug 1 with another cylinder's plug. If the code moves with the plug, replace the plug. If it remains on cylinder 1, suspect wiring or ECM output.
  9. Inspect ECM/driver: if wiring, connectors, fuses, relay, and glow plug are good, inspect the ECM output and related control circuits. Replace or reprogram ECM only after confirming failures.
  10. Repair and verify: repair/replace faulty components (glow plug, wiring, connector, relay, fuse, or ECM), clear codes and perform repeated preheat/start cycles to confirm the fault is resolved.

Likely causes

  • Corroded/broken connector or wiring to glow plug 1 (most common)
  • Failed glow plug (open/high-resistance)
  • Blown fuse or bad glow relay
  • ECM driver fault (rare)
  • Low battery/voltage problem causing abnormal readings

Fault status

⚠️ Status
P0671 — Cylinder 1 Glow Plug Circuit/Open: ECM detected open or abnormally high resistance in the glow plug/heater circuit for cylinder 1 during preheat/operation.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours
320

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