What Does P0671 Mean?
The PCM has detected a malfunction in the cylinder 1 glow plug circuit on a diesel engine. This is a general circuit code indicating the glow plug or its wiring is not functioning correctly — it could be open, shorted, or showing abnormal resistance. Without a properly functioning glow plug, cylinder 1 will not ignite fuel efficiently during cold starts. The driver may notice extended cranking times, rough idle during warm-up, and white exhaust smoke.
Common Causes
40%
Failed cylinder 1 glow plug (burned out or degraded)
25%
Corroded or loose connection at glow plug terminal or bus bar
20%
Wiring fault between glow plug module and cylinder 1 glow plug
10%
Glow plug control module cylinder 1 output failure
5%
Glow plug seized in cylinder head with broken tip
Diagnostic Steps
1
Disconnect the cylinder 1 glow plug and measure its resistance. Typical spec for modern ceramic glow plugs is 0.5-2.0 ohms at room temperature. Compare to adjacent glow plug readings for reference.
2
Check voltage at the glow plug connector during the glow cycle (key on, engine off). Battery voltage or near-battery voltage should be present for the duration of the glow timer.
3
Inspect the bus bar connection at cylinder 1 — tighten the nut to specification (typically 10-15 Nm) and clean any corrosion from the contact surfaces.
4
If the glow plug is suspect, attempt removal after applying penetrating oil and warming the engine. Use a proper glow plug socket to prevent breaking the plug.
5
After replacing the glow plug, clear the code and perform a cold-start test to verify proper operation. Monitor the glow plug current draw with a clamp ammeter (typically 15-25A per plug).
Estimated Repair Cost
$60 - $350
Parts + labor, varies by vehicle and location
The PCM has detected a malfunction in the cylinder 1 glow plug circuit on a diesel engine. This is a general circuit code indicating the glow plug or its wiring is not functioning correctly — it could be open, shorted, or showing abnormal resistance. Without a properly functioning glow plug, cylinde...
The most common cause of P0671 (Cylinder 1 Glow Plug Circuit) is: Failed cylinder 1 glow plug (burned out or degraded)
Typical repair costs for P0671 range from $60 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
One failed glow plug affects cold-start quality but is not dangerous. The engine will run rough until warm and produce white smoke. In extreme cold, the combination of one failed glow plug with marginal battery condition could result in a no-start. Replace promptly before winter.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0671 to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Glow Plug System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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