OBD-II trouble code
P0671: Cylinder 1 Glow Plug Circuit
A fault — usually an open circuit — was detected in the cylinder 1 glow plug circuit on a diesel engine. The most common cause is a failed glow plug or its wiring, affecting cold starting and smooth cold running.
Quick facts
- System
- Powertrain
- Category
- Auxiliary Emissions Controls
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $60 – $400
- DIY difficulty
- Intermediate DIY
What does P0671 mean?
Each cylinder of a diesel engine has a glow plug that pre-heats the combustion chamber for cold starting and clean cold running. The glow plug control module monitors each plug's circuit, and P0671 sets when it detects a fault — most often an open circuit — in the glow plug circuit for cylinder 1 specifically. Unlike the module-level code P0670, P0671 names one cylinder's plug, which usually points at that plug, its connector, or the wire feeding it.
The most common cause is simply a failed (open) cylinder 1 glow plug, since glow plugs wear out and fail over time. Wiring and connector problems at that plug, corrosion, and occasionally a control-module fault can also set it. Because it affects a single cylinder's pre-heating, the practical impact is hard cold starting, a brief rough idle or misfire when cold, and sometimes white smoke until the engine warms; once warm the engine typically runs normally. Diagnosis is straightforward — test the cylinder 1 glow plug and its circuit for continuity and replace the failed plug, checking the connector and wiring along the way.
Common causes
- Failed (open) cylinder 1 glow plug
- Damaged or corroded connector at the cylinder 1 glow plug
- Broken or chafed wiring to the plug
- Poor ground at the glow plug
- Glow plug control module fault affecting the cylinder 1 output
- Previous overheating that fatigued the plug
Symptoms
- Hard cold starting or extended cranking
- Brief rough idle or misfire when cold
- White smoke on cold start until warm
- Check engine light with P0671 stored
- Glow-plug indicator behaving abnormally on some vehicles
Diagnostic steps
- 1.Scan and record all codes; note any other cylinder glow-plug codes or P0670.
- 2.Locate the cylinder 1 glow plug and inspect its connector and wiring for damage and corrosion.
- 3.Test the cylinder 1 glow plug's resistance/continuity against spec — an open plug is the usual cause.
- 4.Check the wire and ground between the plug and the control module for continuity.
- 5.If the plug and wiring are good, evaluate the glow plug control module's cylinder 1 output.
- 6.Replace the failed glow plug (and connector/wiring as needed) and clear the code.
Repair cost
$60 – $400
A single glow plug is inexpensive, but access varies — replacement is often $80-$300 depending on how buried the plug is and whether it comes out cleanly. A seized plug that breaks off raises the cost. Wiring/connector repairs are usually cheaper.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with glow plug / glow plug module replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.