P0671 — Problem with cylinder 1 glow plug electrical circuit

The engine control unit detected an issue with the electrical circuit powering the glow plug in cylinder 1. Glow plugs help start diesel engines by heating the air in the cylinder. This code appears when the glow plug is not receiving proper voltage or is malfunctioning, causing poor starting or rough running in cold conditions.

Common causes

The cause is almost always one of a few things. Here they are — P0671 rarely comes from anything outside this list:

• Faulty or burnt-out glow plug in cylinder 1
• Damaged wiring or connector to the glow plug
• Blown fuse or relay controlling the glow plugs
• Corroded or loose electrical connections

Where to start

In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:

1. Check and replace blown fuses or faulty relays
2. Inspect and repair wiring and connectors
3. Test and replace the glow plug in cylinder 1
4. Clear the code and test drive to confirm repair

That is what holds for P0671 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.