P0671 Code: Cylinder 1 Glow Plug Circuit
The glow plug in cylinder 1 or its wire isn't drawing normal current. Usually the plug itself has burned out.
At a glance
Severity: Low
- Meaning
- Cylinder 1 Glow Plug Circuit
- System
- Ignition & Misfire · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $60–$2,000
- DIY difficulty
- Moderate
On diesels where each glow plug is powered separately, the glow plug control module or engine computer measures the current every plug draws. P0671 means the plug in cylinder 1 is drawing too little current (open), too much (shorted), or none at all. By far the most common reason is a burned-out plug, followed by a corroded connector or a damaged wire. Cylinder 1 is at the timing-belt or chain end of an inline engine, and on Ford Power Stroke V8s it is the front cylinder on the passenger side. The code is simple to diagnose with a meter. The hard part can be removing the plug, because glow plugs that have been in for many years often seize in the cylinder head and snap if forced.
Can I keep driving? Drivable without restrictions once the engine is running. One dead plug mostly shows up as a slightly rougher, smokier cold start. Don't put off the repair indefinitely, though: the longer a plug stays in, the more likely it is to seize.
How to read P0671
- P Powertrain
- 0 Generic (SAE)
- 6 Computer & outputs
- 71 Specific fault
Symptoms
- Slightly longer cranking and a rough first minute on cold mornings
- More white smoke or diesel smell right after a cold start
- Knocking that fades once the engine warms up
- Check-engine or glow plug light, sometimes only in cold weather
- No symptoms at all in warm weather, only the stored code
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Glow plug in cylinder 1 has burned out (open heating element)
- Corroded, loose or burned connector on the cylinder 1 plug
- Wire from the control module to plug 1 damaged or chafed
- Plug 1 shorted internally, with its tip swollen or cracked
- Under-valve-cover harness connector failed (Ford Power Stroke and other engines with internal glow plug wiring)
- Output for cylinder 1 in the glow plug control module failed
Diagnosis step by step
Check the plug's resistance
Disconnect the cylinder 1 glow plug connector and measure from the plug terminal to engine ground. Compare the reading with the other plugs: they should be close to each other, typically well under 2 ohms for metal plugs. An open reading confirms a dead plug. A reading far higher than the others means it is on its way out.
Tools: Multimeter
Check the wire and connector
If plug 1 measures the same as the others, check the wire from the module or relay output to the plug connector: under 1 ohm end to end and not shorted to ground. Look for green corrosion inside the push-on connector, which is common where engine washes or rain reach it.
Tools: Multimeter, Flashlight
Compare the current draw
During a glow cycle, clamp a DC current meter around each plug's wire in turn. A healthy plug draws much the same as its neighbors, and a dead one draws nothing. This confirms the diagnosis without taking anything apart.
Tools: Multimeter
Remove the plug the safe way
Remove glow plugs with the engine at operating temperature, after soaking the threads with penetrating oil, ideally over several days. Use a deep socket and a torque wrench or a click-type breakaway tool. If the plug doesn't turn at the maker's limit, often around 15 to 25 Nm for common sizes, stop and let it soak again rather than forcing it.
Tools: Torque wrench, Gloves
If it won't come out, get specialist help
A plug that snaps off in the head can usually be drilled and extracted with a dedicated kit, often without removing the head. It is time-consuming work, and debris must not fall into the cylinder. A shop with the extraction kit is cheaper than a cylinder head job.
Tools: Flashlight
Fit the new plug correctly
Clean the bore, fit the correct plug for your engine and tighten it to the specified torque, which is low. Overtightening can damage the thin tip or the head. Reconnect, clear the code and confirm on a cold start that no code returns.
Tools: Torque wrench, OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace cylinder 1 glow plug (comes out normally) | Yes | $80–$220 |
| Replace all glow plugs at once | No | $180–$600 |
| Repair glow plug connector or wire | No | $60–$200 |
| Replace under-valve-cover glow plug harness (Power Stroke) | No | $300–$900 |
| Drill out and extract a snapped glow plug | No | $500–$2,000 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Ford
On the 6.0L Power Stroke the glow plugs are fed through a harness under each valve cover. Its connectors at the glow plugs and at the valve cover gasket often fail, setting glow plug codes such as P0671 even when the plug is fine. Measure through the valve cover connector and at the plug before blaming the plug.
Mercedes-Benz
Mercedes CDI diesels, including those in the Sprinter, are well known for glow plugs seizing in the aluminum cylinder head. Forcing a stuck plug on these engines risks snapping it, so shops typically soak the threads, warm the engine and use a controlled-torque tool.
Emissions / smog test impact
Depends
Glow plug circuit codes affect an emissions inspection only where diesels are tested and the code turns on the check-engine light. Many programs don't test diesels at all, but where light-duty diesels get an OBD check, a lit check-engine light fails.
Frequently asked questions
Can one dead glow plug stop the engine from starting?
Rarely on its own. The other plugs heat their cylinders, and once the engine turns over, cylinder 1 catches up. You'll notice a rougher, smokier first minute, and in hard frost starting may take noticeably longer.
Why did my glow plug snap on removal?
Years of heat and combustion deposits bond the thread and the tip to the head. Force or a rushed job without penetrating oil and a warm engine breaks the plug's thin body. Stop at the maker's torque limit and let it soak again.
Should I replace all the glow plugs?
If they come out easily and are old, yes, they wear at similar rates. On engines prone to seizing, many shops only replace the dead one, because every removal carries a risk of snapping.
Is cylinder 1 always at the front of the engine?
On an inline diesel it is the cylinder at the timing-belt or chain end, which in a transverse engine is at the side of the engine bay, not the front of the car. On Ford Power Stroke V8s it is the front cylinder on the passenger side.