P0671: Cylinder 1 Glow Plug Circuit

P0671 is a diesel-only code meaning the engine control unit detected an electrical fault in the glow plug circuit for cylinder 1. Glow plugs preheat each combustion chamber so a cold diesel can ignite. The code identifies the cylinder 1 circuit specifically, usually pointing to a failed plug, its wiring, or its connection rather than the whole system. Repairs typically run 30-180 EUR for a single plug and circuit fix.

P0671 is a electrical-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0671 and illuminates the check engine light.

If your vehicle has triggered P0671, you may notice one or more of these symptoms:

• Check engine light or glow plug indicator illuminated
• Harder cold starts, especially in cold weather
• Brief cold misfire or stumble from cylinder 1 after startup
• White or grey smoke from the exhaust on cold start
• Longer cranking time before the engine catches
• Will likely fail a diesel technical or emissions inspection

Here are the most common causes of P0671, ranked by how likely they are to be the culprit:

Generally yes, for short-term driving. Safe to drive once the engine is warm. This code flags the glow plug circuit for cylinder 1 only, and a single failed plug rarely stops a diesel from running. Expect harder cold starts, longer cranking, and a brief cold misfire from cylinder 1 with more white startup smoke. The car will likely fail a diesel inspection with this code stored.

Follow these steps to pinpoint the root cause of P0671:

1. Read the stored code and freeze frame with Skanyx or any ELM327 adapter to confirm P0671 and note the start temperature when it set
2. Locate the cylinder 1 glow plug and inspect its connector and wiring for corrosion, looseness, or damage
3. Disconnect the cylinder 1 glow plug and bench-test it with a multimeter: a healthy plug reads roughly 0.5-2 ohm, while an open (infinite) reading confirms that plug has failed
4. If the cylinder 1 plug is good, check continuity of its wiring back to the control module and verify a clean ground
5. Remember that per-cylinder glow plug live status is manufacturer-extended (Mode $22) data, not generic OBD2, so the multimeter test on the cylinder 1 plug is how you confirm the failure
6. Consider replacing the full set if the plugs are original and high-mileage, since the others are likely to fail soon

Repair costs for P0671 vary depending on the root cause and your vehicle. Here are typical estimates:

P0671 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:

These codes are often seen alongside P0671 or indicate related issues: