Failed cylinder 1 glow plug (both sources). Open or shorted wiring in the cylinder 1 glow plug circuit (both sources). Damaged or corroded connector at the glow plug or module (OBD-Codes.com, Jeep service manual). Faulty glow plug control module (both sources).

Replace the cylinder 1 glow plug; RepairPal lists glow plug replacement as the common repair. Repair or replace the damaged glow plug wire, lead or connector. Replace a faulty glow plug control module after the plug and wiring test good (both sources; the Jeep manual tests plug and wiring first). Clear the code and confirm it does not return.

P0671🔧 Diesel cold-start / glow plug systemStop and fix promptly

P0671: Cylinder 1 Glow Plug Circuit (Meaning, Causes, Fixes)

Q: What does P0671 mean?

P0671 is a diesel-engine code: the engine computer has found a fault in the circuit of the glow plug for cylinder 1, so that plug isn't heating up. The usual causes are a burned-out cylinder 1 glow plug, damaged wiring or a connector to it, or a faulty glow plug control module, and the result is harder starting in the cold. Diesel engines ignite fuel with the heat of compressed air, and on a cold engine that heat is lost to the cold cylinder head. Glow plugs, small electric heaters in each cylinder, warm the combustion chamber for a few seconds so the engine can start. OBD-Codes.com explains that the engine computer decides when to run them using engine temperature sensors and powers them through a glow plug module and relay. P0671 means something in the circuit for the cylinder 1 glow plug is faulty, so that plug fails to heat. The sources word the definition slightly differently: OBD-Codes.com calls it 'Cylinder #1 Glow Plug Circuit', while RepairPal and the 2014 Jeep Wrangler (2.8L diesel) factory service manual call it 'Cylinder 1 Glow Plug Circuit/Open'. The Jeep manual says its version sets when the PCM detects an open on the cylinder 1 glow plug circuit while the glow plugs are commanded on. OBD-Codes.com adds that if P0670 (glow plug control module circuit) is also stored, diagnose P0670 first. Note that which cylinder is 'cylinder 1' depends on the engine; check your service manual.

Q: Can I keep driving with P0671?

Stop and fix promptly. RepairPal rates P0671 urgent, meaning immediate action is needed, and lists hard or no starting in cold weather as the main symptom. OBD-Codes.com is milder: it says that with just one failed glow plug the symptoms are usually minimal and the engine normally still starts, with trouble most likely in freezing weather. Either way, the risk is being unable to start on a cold morning, so get it checked before winter.

Reviewed 2026-10-22 · Based on 3 cited source(s)

What P0671 means

Diesel engines ignite fuel with the heat of compressed air, and on a cold engine that heat is lost to the cold cylinder head. Glow plugs, small electric heaters in each cylinder, warm the combustion chamber for a few seconds so the engine can start. OBD-Codes.com explains that the engine computer decides when to run them using engine temperature sensors and powers them through a glow plug module and relay. P0671 means something in the circuit for the cylinder 1 glow plug is faulty, so that plug fails to heat. The sources word the definition slightly differently: OBD-Codes.com calls it 'Cylinder #1 Glow Plug Circuit', while RepairPal and the 2014 Jeep Wrangler (2.8L diesel) factory service manual call it 'Cylinder 1 Glow Plug Circuit/Open'. The Jeep manual says its version sets when the PCM detects an open on the cylinder 1 glow plug circuit while the glow plugs are commanded on. OBD-Codes.com adds that if P0670 (glow plug control module circuit) is also stored, diagnose P0670 first. Note that which cylinder is 'cylinder 1' depends on the engine; check your service manual.

Severity: can I keep driving?

Stop and fix promptly

RepairPal rates P0671 urgent, meaning immediate action is needed, and lists hard or no starting in cold weather as the main symptom. OBD-Codes.com is milder: it says that with just one failed glow plug the symptoms are usually minimal and the engine normally still starts, with trouble most likely in freezing weather. Either way, the risk is being unable to start on a cold morning, so get it checked before winter.

Common symptoms

Check engine light on; OBD-Codes.com says the code is often the main sign, since one bad plug causes few symptoms
Hard starting or no start in cold weather (both sources)
Lack of power, a miss, or hesitation until the engine warms up (OBD-Codes.com)
Preheat (glow plug) light not going off as normal (OBD-Codes.com)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Failed cylinder 1 glow plug (both sources)
Open or shorted wiring in the cylinder 1 glow plug circuit (both sources)
Damaged or corroded connector at the glow plug or module (OBD-Codes.com, Jeep service manual)
Faulty glow plug control module (both sources)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

If P0670 is also stored, deal with that first, as OBD-Codes.com advises.
Inspect the wire and connector at the cylinder 1 glow plug for looseness, cracks, corrosion or missing insulation.
With the connector off, measure the glow plug's resistance from its terminal to a good ground. OBD-Codes.com gives a typical range of 0.5 to 2.0 ohms, while the 2014 Jeep Wrangler 2.8L diesel manual allows 0.2 to 5.0 ohms; an open (infinite) reading means the plug has failed. Use the spec in your own service manual.
Check the wire from the glow plug module or bus bar to the cylinder 1 plug for high resistance; OBD-Codes.com notes these leads are often fusible links.

Typical fixes

Replace the cylinder 1 glow plug; RepairPal lists glow plug replacement as the common repair
Repair or replace the damaged glow plug wire, lead or connector
Replace a faulty glow plug control module after the plug and wiring test good (both sources; the Jeep manual tests plug and wiring first)
Clear the code and confirm it does not return

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

Following the factory procedure: the Jeep manual checks the circuit resistance between the glow plug connector and the module connector, then the plug itself, then the wiring and module
Checking for technical service bulletins for your engine, as the Jeep manual advises
Removing a seized glow plug carefully; many shops do this to avoid breaking a plug off in the cylinder head

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with P0671?

Usually yes once the engine is running; OBD-Codes.com says one bad glow plug causes minimal symptoms and the engine normally still starts. RepairPal still rates it urgent because cold starts can fail, so fix it before cold weather.

Does P0671 happen on gas engines?

No. Glow plugs are a diesel part, so this code is for diesel engines.

Should I replace all the glow plugs?

The sources only say to replace the plug that tests bad. Some owners replace all of them at once on high-mileage engines, but that's a choice, not a requirement from these sources.

Sources

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.