Diesel P0671: Cylinder 1 Glow Plug Circuit Malfunction
P-Code P0671 (FMI N/A) — Cylinder 1 Glow Plug Circuit Malfunction
Quick Answer
P0671 means a fault specifically in the cylinder 1 glow plug circuit, typically an individual plug failure rather than a broader control module issue.
Overview: Universal Diesel P-Code P0671
This is a more isolated fault than a module-level glow plug code. Testing the individual plug's resistance is usually all that's needed to confirm the diagnosis.
Repair Snapshot
Time
1 - 2 Hours
Difficulty
Beginner
Parts Cost
$30 - $150
Dealer Labor
$250+
Tools Required
- Multimeter
- Socket Set
- Anti-Seize Compound
What P-Code P0671 Means
P0671 means the PCM detected a fault specifically in the cylinder 1 glow plug circuit, as opposed to a broader module-level fault. This is typically an individual glow plug failure or a wiring issue isolated to that one cylinder's circuit.
Symptoms Drivers Notice
- Harder cold starts, though usually less severe than a full module fault since only one cylinder is affected
- Slightly more white smoke on cold startup
- Check engine light
- Minor rough idle when cold, smoothing out as the engine warms
Most Likely Root Causes
Failed individual glow plug
CommonGlow plugs wear out over time and can fail individually.
Corroded connector at cylinder 1
CommonDisrupts power delivery to that specific glow plug.
Damaged wiring isolated to this cylinder
OccasionalA localized wiring fault affecting just this circuit.
Common Misdiagnoses (Don't Waste Parts)
Replacing all glow plugs when only one has failed
Why it happens: It seems efficient to do them all at once.
Do this instead: Test each plug's resistance individually - replacing only the failed one saves cost if others are healthy.
Overlooking the connector
Why it happens: Focus goes straight to the plug itself.
Do this instead: Check the connector for corrosion before assuming the plug has failed.
Master Tech Commentary
Mechanic's Notes
Shop tip: glow plugs can be brittle when removed, especially on higher-mileage engines. Use anti-seize on the replacement and remove carefully to avoid a snapped plug tip in the cylinder head.
Step-by-Step Diagnostic Procedure
- Step 1: Locate the cylinder 1 glow plug and inspect its electrical connector for corrosion.
- Step 2: Check the individual glow plug's resistance with a multimeter against specification.
- Step 3: Inspect the wiring from the control module to this specific glow plug for damage.
- Step 4: Test for proper voltage reaching the glow plug when commanded on.
- Step 5: Replace the glow plug if resistance is out of spec and wiring checks out clean.
Live Data & Freeze-Frame Tips
Use a multimeter to check resistance on the individual glow plug and compare against specification - an open circuit or wildly out-of-spec reading confirms plug failure.
Safety Warnings
- Allow the engine to cool before removing glow plugs.
- Use care when removing glow plugs on higher-mileage engines to avoid breakage.
When to Limp In vs Tow
Not required - the truck remains driveable, though cold starts may be slightly harder.
Prevention Tips for Fleets & Owner-Operators
- Replace glow plugs as a set if others are approaching end of service life.
- Inspect connectors during routine maintenance.
- Address hard-start symptoms before winter.
Related Fault Codes
P0670
Glow plug module control circuit fault, a broader version affecting all plugs together.
Frequently Asked Questions
Do I need to replace all the glow plugs?
Not necessarily - if only cylinder 1's plug has failed, replacing just that one is often sufficient.
Is this an expensive repair?
Usually inexpensive - individual glow plugs are a low-cost part.
Can I drive with this code?
Yes, though cold starts may be slightly harder than normal.
How do I test a glow plug myself?
A multimeter resistance check against the plug's specification is usually sufficient.
Will this affect summer driving?
Minimally - glow plugs matter most for cold starts.