P0671 Cylinder 1 Glow Plug Circuit

P0671 indicates a cylinder 1 glow plug circuit fault. The controller sees an electrical problem in the glow plug circuit for cylinder 1.

Code details

Generic OBD-II · P0

System: Computer
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace multiple glow plugs without comparing cylinder 1 measurements against the remaining cylinders.

Symptoms of P0671

Check-engine light, sometimes with several unrelated codes at once.
Warning lights, a no-start, or intermittent electrical faults.
Communication or module-reset problems on a scan tool.

Common causes of P0671

Low battery voltage, poor grounds, corroded connectors, or blown fuses.
Wiring or network (CAN bus) faults between modules.
A module software/programming issue, or rarely a failed controller.

Useful checks before replacing parts

Check cylinder 1 glow plug resistance, command voltage, current draw, connector condition, battery voltage, coolant temperature, and freeze-frame data.
Inspect the cylinder 1 glow plug lead, terminal tightness, module output, harness heat damage, corrosion, and shorts to ground or power.
Compare cylinder 1 current and resistance against known good cylinders to separate a failed plug from wiring or module output faults.

Related OBD-II codes

These nearby computer entries can help compare wording and pin down the fault area.