Failed glow plug (open internal element); Damaged or corroded electrical connector at the glow plug; Broken or chafed wiring in the glow plug circuit; Faulty glow plug control module (GPCM) or relay; Poor ground connection for the glow plug circuit; ECM internal fault (rare)

DTC codes / P06xx · Computer and output circuits / P0671

P0671Cylinder 1 Glow Plug Circuit

Q: What does code P0671 mean?

Cylinder 1 Glow Plug Circuit. P0671 indicates that the engine control module (ECM) has detected an open circuit, short to ground, or short to voltage on the glow plug circuit for cylinder 1. This code is specific to diesel engines that use glow plugs for cold-start assistance, and it means the electrical path to that glow plug is not functioning as expected.

P0671 indicates that the engine control module (ECM) has detected an open circuit, short to ground, or short to voltage on the glow plug circuit for cylinder 1. This code is specific to diesel engines that use glow plugs for cold-start assistance, and it means the electrical path to that glow plug is not functioning as expected.

SystemPowertrain

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaComputer and output circuits

Symptoms you may notice

Illuminated check engine light or glow plug warning lamp
Hard starting or rough idle when the engine is cold
Excessive white smoke from the exhaust after a cold start
Engine misfire or stumbling during the first few minutes of operation
Often no symptoms besides the warning light, especially in mild weather

Common causes, most likely first

Failed glow plug (open internal element)
Damaged or corroded electrical connector at the glow plug
Broken or chafed wiring in the glow plug circuit
Faulty glow plug control module (GPCM) or relay
Poor ground connection for the glow plug circuit
ECM internal fault (rare)

How to diagnose and fix it

Inspect the glow plug connector and wiring for damage, corrosion, or looseness
Measure the resistance of the glow plug with a multimeter and compare to specification
Check for battery voltage at the glow plug connector during the glow plug preheat cycle
Test the glow plug control module or relay for proper operation
Repair or replace any damaged wiring or connectors
Replace the faulty glow plug if resistance is out of range
Clear the code and verify the repair with a test drive and re-scan

Glow plug circuit checks that save time

A glow plug that tests good on resistance can still fail under load, so always verify voltage drop across the circuit while the glow plugs are commanded on.
Corrosion inside the glow plug connector boot is a frequent cause of P0671 that is easily overlooked during a visual inspection.
The glow plug control module often fails in ways that set codes for multiple cylinders, but a single-cylinder code like P0671 usually points to the plug or its wiring.
On some vehicles, the glow plug circuit is monitored only during the initial key-on preheat cycle, so an intermittent fault may not set the code until the next cold start.
Replacing a glow plug without checking the control module can lead to repeat failures if the module is supplying excessive voltage.

Can I keep driving with P0671?

You can generally drive with P0671, but cold starting may be difficult and the engine may run rough until warm. Avoid extended driving with a misfire, and address the issue before cold weather to prevent starting problems.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.