P0671: Cylinder 1 Glow Plug Circuit / Open Circuit
Diagnostic Trouble Code (DTC) P0671 indicates that the Engine Control Module (ECM/PCM) or electronic Glow Control Unit (GCU) has detected an electrical open circuit, excessive electrical resistance, or continuity failure isolated specifically to the Cylinder 1 glow plug circuit. In modern diesel engines, each glow plug receives an independently monitored and switched current feed from the electronic glow controller. During pre-heating and post-heating phases, the internal current-sensing shunt resistor dedicated to Cylinder 1 detects that current flow is near zero (< 1.0 A) when energized, indicating a burned-out heating filament inside the Cylinder 1 glow plug, a disconnected connector cap, or a severed wiring harness line.
🚗 Operational Safety, Typical Repair Costs & Diagnostic Verification
- 01
🚦 Driving Safety & Operational Risk
Immediate mechanical assessment and tow requirementsCylinder 1 Glow Plug Circuit Open - Cold Starting Deficit & DPF Regeneration Block
Cylinder 1 glow plug heating element is open-circuit (burned out). While the engine will start in warm weather, cold starts will produce misfires and white smoke. Crucially, the ECU will suspend active DPF regeneration cycles.
MECHANICAL HAZARDS & ENGINE RISK IF DRIVEN:Suspended DPF regenerations lead to soot overload (P2463) and eventual costly DPF filter replacement. - 02
💰 Typical Workshop Repair Budget
Expected parts replacement and garage labor cost tiersMinor DIY / Filter Purge$25 - $60 (DIY Replacement of Cylinder 1 Glow Plug with Bosch/NGK/BERU Part)Sensor cleaning, fuel filter renewal, fuse replacement, or harness contact cleaning.
Sensor / Valve Replacement$90 - $220 (Replacement of All 4 Glow Plugs to Prevent Cascading Failure)Single component fix (e.g. pressure regulator valve, inlet metering unit, or reconditioned injector).
Major Overhaul / Pump & Injectors$350 - $850 (Specialist Tool Labor to Extract Seized/Snapped Glow Plug if Broken in Head)High-pressure injection pump overhaul, new OEM injector set, or DPF assembly replacement.
- 03
🧰 Initial Visual & Physical Verifications
5-minute zero-tool garage triage steps before calling a workshop11. Measure resistance with multimeter: Disconnect cap on Cylinder 1 glow plug, place one probe on center terminal and one on engine block ground (good plug: 0.6 - 1.5 ohms; burned plug: infinite / OL).22. Never attempt removal on a cold engine: Always warm engine to 80 deg C and apply penetrating lubricant 24 hours prior.33. Observe torque limit: Do not exceed 25-30 N-m breaking torque during removal to prevent snapping plug tip. - 04
🛡️ Diagnostic Verification & Mechanic Shield
Exact questions to ask your technician to prevent unnecessary parts replacement""Please confirm resistance of Cylinder 1 glow plug with an ohmmeter before replacing the glow plug control module.""
""Always use high-temperature ceramic anti-seize paste on new plug threads and torque to factory 10-15 N-m.""
""Check that DPF regeneration status resumes to normal after clearing the glow plug fault code.""
Technical Note: Read these technical questions to your mechanic before approving expensive parts replacements:
30-Second Workshop Triage
- Check Engine Light (MIL) and amber spiral glow plug indicator illuminated on the dashboard
- Engine stumbling, rough idle, and misfiring on Cylinder 1 for 15-45 seconds following a cold start
- Puffs of unburned white or grey exhaust smoke during cold starting with a strong smell of raw diesel fuel
- Burned out, fractured, or open internal heating filament inside the Cylinder 1 glow plug
- Loose, disconnected, or corroded electrical connector cap on the Cylinder 1 glow plug terminal
- Broken, chafed, or melted wiring harness wire between the Glow Control Unit and Cylinder 1 glow plug
Connect scan tool live telemetry: compare Target Fuel Rail Pressure vs Actual Rail Pressure and log metering valve command PWM duty cycle during idle and road load.
Expensive Diagnostic Pitfall & Technical Reality
P0671 requires replacing all 4/6 glow plugs immediately, and if plug 1 is seized in the head, the entire cylinder head must be removed ($1,200 - $2,500).
P0671 is an isolated circuit fault specific to Cylinder 1. It means the glow plug control module measured infinite resistance (open circuit) on Cylinder 1's heater circuit. In over 85% of cases, the other cylinders' glow plugs are completely healthy and should NOT be disturbed (unnecessarily disturbing healthy plugs risks shearing them in the head). The root cause is a burned-out heating element inside plug 1 or a loose push-on connector boot that has vibrated off.
Risking head removal and high-cost glow plug extraction ($1,500+) by forcing all plugs out vs testing plug 1 with a $15 multimeter and replacing only the single $18-$35 plug with proper vibration-warm extraction technique, saving over $1,400.
Most Common Engines & Fuel Injection Platforms Affected
This fault code predominantly affects the following common rail diesel platforms. Cross-reference your specific engine family below for verified factory failure modes, key sub-assembly part numbers, and dedicated repair links:
Volkswagen / Audi 2.0 TDI (EA189 / CFFB / CFGB)
Bosch EDC17 Common Rail SystemKnown Factory Failure Mode: Piezo stack degradation, injector harness terminal fretting, DPF differential pressure sensor silicone tube split.
03L130277, 0445110369, 076906051ARenault / Opel 1.9 dCi (F9Q)
Bosch EDC15 / EDC16 Common Rail SystemKnown Factory Failure Mode: Injector harness connector diesel seepage, glow plug tip carbon seizure, EGR valve soot accumulation.
7700107165, 0445110021, 8200542997BMW 2.0d / 3.0d (N47 / N57 / M57TU2)
Bosch CRI2.5 / CRI3.0 Common RailKnown Factory Failure Mode: Injector balance drift beyond +/- 4.0 mg/stroke, glow plug control unit (BERU) power lead failure, DPF backpressure accumulation.
13537805428, 0445116024, 12217801201Ford / PSA 1.6 TDCi / HDi (DV6ATED4 / DLD-416)
Bosch CRI2-16 Common Rail SystemKnown Factory Failure Mode: Injector copper washer blow-by (black death), injector cylinder circuit fretting corrosion, DPF pressure pipes heat cracking.
0445110239, 1980J7, 1618LPDiesel Glow Plug Diagnostics & Circuit Troubleshooting Guide
Workshop troubleshooting guide for diesel glow plug fault codes P0380, P0670, and P0671 to P0674. Resistance specs, GPCM relay testing, and removal torque.
Control Circuit & Actuator Logic
1. Dynamic In-Demand Fuel Metering
The Cylinder 1 glow plug is threaded directly into the cylinder head with its heating tip protruding into the combustion chamber adjacent to the common rail fuel injector nozzle. It receives current via a dedicated wire running from Channel 1 of the Glow Control Unit. The outer steel casing of the glow plug provides the electrical ground return through its threads directly into the engine block. When energized, current flows through an internal heating and regulating coil, heating the tip to over 1,000°C in under 2 to 4 seconds.
2. Closed-Loop PID Deviation Monitoring
The GCU's internal microprocessor monitors instantaneous current on the Cylinder 1 output MOSFET on every activation cycle. Under normal conditions, inrush current peaks at 15A-25A and stabilizes at 8A-12A. If current fails to exceed 1.0 A within 200 milliseconds of activation (indicating infinite resistance / open circuit), the GCU registers a Channel 1 fault and transmits this status to the ECM over the LIN-bus, setting DTC P0671 and turning on the glow plug warning light.
3. Diagnostic Trap: Normally Open (NO) vs Normally Closed (NC) Valves
Open Circuit Isolation Rule: An open circuit on Cylinder 1 glow plug causes cold-start stumbling and white smoke isolated to Cylinder 1. Once the engine warms up, the fault disappears from driveability, but the DTC remains stored in the ECM. The most common cause is a burned-out heating filament inside the plug, which can be verified in under 60 seconds with an ohmmeter.
Electrical & Hydraulic Physical Benchmarks
Step-by-Step Workshop Diagnostic Protocol
Measure Cylinder 1 Glow Plug Resistance In-Place
Turn ignition OFF and pull the electrical connector cap off the Cylinder 1 glow plug. Set a digital multimeter to the lowest resistance scale (200 Ω) and zero the test leads. Touch one probe to the glow plug center terminal pin and the other probe to clean metal on the cylinder head. A healthy standard plug reads 0.6-1.2 Ω (low-voltage ceramic reads 0.3-0.5 Ω). An infinite reading (OL / > 10 Ω) confirms that the glow plug filament is burned open and must be replaced.
Test Harness Voltage Output from Glow Control Unit
Connect a 12V test light (or digital multimeter) between the Cylinder 1 glow plug harness cap and cylinder head ground. Turn ignition ON with a cold engine. The test light must illuminate brightly (or multimeter show battery voltage / PWM pulse) for 2 to 5 seconds. If power is present at the cap but the plug is open, replacing the plug resolves the issue.
Harness Continuity & Load Test to GCU
If no voltage was measured at the harness cap, disconnect the output connector at the Glow Control Unit. Using a digital multimeter, test continuity on the wire from the GCU Channel 1 pin to the Cylinder 1 glow plug connector (must read < 0.3 Ω). Perform a dynamic load test using a 21W automotive bulb to verify that the wire can support current without high-resistance voltage drops.
Test Glow Plug Terminal Ground Path Through Cylinder Head
Measure resistance between the outer hexagonal steel body of the glow plug and the battery negative terminal. Resistance must be < 0.1 Ω. If excessive resistance is found, corrosion or thread sealant on the glow plug threads is preventing electrical ground return.
Safe Removal & Torque Limit Inspection
If replacing the plug, warm the engine to operating temperature (> 80°C). Spray high-grade penetrating fluid around the glow plug base. Use a calibrated torque wrench set to 20 Nm (M8) or 35 Nm (M10). Gently apply counter-clockwise pressure. If the plug turns freely, remove it; if it binds, turn it back clockwise slightly and re-apply penetrating fluid to work carbon out of the threads.
New Glow Plug Installation & Thread Preparation
Before installing a new glow plug, ream the carbon out of the glow plug aperture using an OEM reamer tool greased to catch carbon flakes. Apply a tiny smear of high-temperature ceramic anti-seize paste to the threads (avoiding the heating tip). Tighten to specified factory torque (typically 12-15 Nm for M8, 15-20 Nm for M10).
Component-Level BOM: Cylinder 1 Cold-Start Preheating Subsystem
Cylinder 1 Cold-Start Preheating Subsystem
0 250 403 008 / Beru GE101 / OEM Glow Plug
Reaches 1,000°C tip temperature within 3 seconds to facilitate compression ignition
OEM Silicone Glow Cap Wire Repair Pigtail
Provides corrosion-resistant high-current contact to the glow plug terminal pin
Beru GKF01 / Liqui Moly 3418 Ceramic Paste
Prevents galvanic corrosion and thread seizure between glow plug steel threads and aluminum cylinder head
Glow Plug Resistance & Current Draw Inspector
Associated Fuel Injection Components
The following genuine OEM fuel pumps and common rail injectors are verified factory equipment for engines reporting fault protocol P0671. Cross-reference operating pressures and tightening torques before sub-assembly replacement:
0445110021BOSCH
BOSCH 0445110021 - F9Q 1.9 dCi Common Rail Injector
View Technical Specs & Fitment →0445110239BOSCH
0445110239 Injector: PSA 1.6 HDi Ford 1.6 TDCi Specs
View Technical Specs & Fitment →0445110369BOSCH
0445110369 Injector: VW 2.0 TDI EA189 CFFB CFHC Specs
View Technical Specs & Fitment →0445116024BOSCH
BOSCH 0445116024 Common Rail Piezo Injector for BMW N47 2.0d & N57 3.0d
View Technical Specs & Fitment →High-Pressure Pump Adaptation Reset & Road Test Drive Cycle
Following the replacement of the Cylinder 1 glow plug or harness repair for DTC P0671:
1. Clear all stored trouble codes from the Engine Control Module using an OBD-II diagnostic tool.
2. Access ECM Special Functions -> 'Glow Plug Adaptation / Reset Learned Resistance' (if required on vehicle platform).
3. Switch ignition OFF and leave undisturbed for 30 seconds to allow the ECM and GCU to register the cleared fault status.
4. Perform a cold soak test: let the engine cool, switch ignition ON, and verify that the spiral glow light illuminates and turns off normally.
5. Start the engine and verify smooth combustion on Cylinder 1 without cold-start shaking or white smoke.
Differential Diagnosis & Related Faults
Workshop Field Case Studies
2015 Volkswagen Golf 1.6 TDI (EA288 CLHA)(168,000 km)
Frequently Asked Technical Questions
What does engine fault code P0671 mean?
Diagnostic Trouble Code (DTC) P0671 indicates that the Engine Control Module (ECM/PCM) or electronic Glow Control Unit (GCU) has detected an electrical open circuit, excessive electrical resistance, or continuity failure isolated specifically to the Cylinder 1 glow plug circuit. In modern diesel engines, each glow plug receives an independently monitored and switched current feed from the electronic glow controller. During pre-heating and post-heating phases, the internal current-sensing shunt resistor dedicated to Cylinder 1 detects that current flow is near zero (< 1.0 A) when energized, indicating a burned-out heating filament inside the Cylinder 1 glow plug, a disconnected connector cap, or a severed wiring harness line.
What are the most common symptoms of P0671?
Check Engine Light (MIL) and amber spiral glow plug indicator illuminated on the dashboard, Engine stumbling, rough idle, and misfiring on Cylinder 1 for 15-45 seconds following a cold start, Puffs of unburned white or grey exhaust smoke during cold starting with a strong smell of raw diesel fuel, Slightly longer cranking time before the engine fires up when temperatures are near or below freezing, Active DPF soot regeneration blocked on some vehicle platforms, leading to eventual soot accumulation, Diagnostic scan tool reports 'Cylinder 1 Glow Plug Circuit Open / Electrical Malfunction'.
What causes P0671 on a diesel engine?
Burned out, fractured, or open internal heating filament inside the Cylinder 1 glow plug; Loose, disconnected, or corroded electrical connector cap on the Cylinder 1 glow plug terminal; Broken, chafed, or melted wiring harness wire between the Glow Control Unit and Cylinder 1 glow plug; Blown internal output driver MOSFET channel for Cylinder 1 inside the Glow Control Unit (GCU); Severe carbon buildup or corrosion on the glow plug threads preventing adequate electrical grounding to the cylinder head; Water intrusion in the glow plug harness boots causing terminal pin oxidation and contact loss.
Is it safe to drive with code P0671 active?
🟡 Caution: Limp Mode Active / Service Soon
How much does it cost to fix fault code P0671?
Typical repair costs for fault code P0671 depend on the underlying root cause and diagnostic tier: Level 1 (Minor / Maintenance): $25 - $60 (DIY Replacement of Cylinder 1 Glow Plug with Bosch/NGK/BERU Part) (Sensor cleaning, fuel filter renewal, fuse replacement, or harness contact cleaning.); Level 2 (Component Replacement): $90 - $220 (Replacement of All 4 Glow Plugs to Prevent Cascading Failure) (Single component fix (e.g. pressure regulator valve, inlet metering unit, or reconditioned injector).); Level 3 (Major Sub-Assembly): $350 - $850 (Specialist Tool Labor to Extract Seized/Snapped Glow Plug if Broken in Head) (High-pressure injection pump overhaul, new OEM injector set, or DPF assembly replacement.). Independent workshop benchmark rates. Data indicates over 70% of occurrences are resolved within Level 1 or Level 2 without replacing entire sub-assemblies.
Can I continue driving with DTC P0671 active?
Yes, once the engine is warm, the glow plug plays no role in normal combustion, so the vehicle will drive with normal power and economy. However, in cold weather, the engine will start hard with Cylinder 1 misfiring and smoking. Additionally, some vehicles disable DPF regeneration while any glow plug code is active, which will eventually clog the DPF.
Should I replace all glow plugs when only Cylinder 1 has code P0671?
Yes, strongly recommended. All glow plugs endure the exact same number of thermal cycles, cold starts, and combustion exposures. When one plug burns open, the remaining plugs are usually near the end of their operational lifespan.
Can I test the glow plug without removing it from the engine?
Yes! Simply unplug the wiring cap from the top of the Cylinder 1 glow plug. Use a digital multimeter on the 200 Ω scale: place the positive probe on the center terminal pin and the negative probe on the engine cylinder head metal. If it reads OL (infinite resistance), the plug is 100% burned out and must be replaced.