Ignition and pre-heatingGeneric OBD-II codeUrgency: Garage soon
Code P0671: glow plug circuit, cylinder 1
P0671 means: glow plug (heater) circuit, cylinder 1.[1][2][3] The ECU (or the glow plug module) has detected an electrical fault in the glow plug circuit, also called the heater, of cylinder 1. TaT describes it as an open circuit, that is, an interrupted electrical path; TroubleCodes.net as a fault that breaks the continuity of the control circuit or causes a voltage variation of 10% or more; and Ross-Tech lists it, on VAG group TDIs, as an "electrical fault" in the cylinder 1 glow plug circuit.[1][2][3]
What code P0671 means
The ECU (or the glow plug module) has detected an electrical fault in the glow plug circuit, also called the heater, of cylinder 1. TaT describes it as an open circuit, that is, an interrupted electrical path; TroubleCodes.net as a fault that breaks the continuity of the control circuit or causes a voltage variation of 10% or more; and Ross-Tech lists it, on VAG group TDIs, as an "electrical fault" in the cylinder 1 glow plug circuit.[1][2][3]
It only affects diesel engines. Glow plugs heat the combustion chamber to make cold starting easier and there is one per cylinder, so if the cylinder 1 circuit is open, that glow plug does not heat up.[1][3][4]
The code points to that plug's circuit, not to a specific part: according to TaT, it is usually due to a faulty glow plug or a poor connection at that cylinder. Codes P0672, P0673 and P0674 are the same fault on cylinders 2, 3 and 4.[1][5][6][7]
It is a generic OBD-II code (it starts with P0), so it means the same on any make; what changes from one engine to another is the most likely cause.[8]
Original definition (SAE J2012): Cylinder 1 Glow Plug Circuit[1][2][3]
Codes from the same family
They indicate the same problem in a specific cylinder, bank or sensor. Causes, symptoms and diagnosis are those on this page.
Causes of P0671 and its family
From most to least likely, according to the sources.
- 1Faulty cylinder 1 glow plug, with the heating element broken (open circuit). TaT and Ross-Tech cite it among the main causes, and Klavkarr explains that a burnt-out glow plug reads infinite resistance.[1][2][3][9]
- 2Damaged wiring and connectors on that glow plug: damaged or disconnected wires, corroded connectors or poor connections.[1][2][3]
- 3Faulty glow plug relay or timer, on older systems.[3][10]
- 4Faulty glow plug control module. Klavkarr identifies it, along with the glow plug with an open circuit, as one of the two main causes of codes P0380 and P0670.[3][9]
- 5Engine ECU fault (TroubleCodes.net describes it as rare in its P0672 entry).[3][10]
Symptoms
- Cold starting that is longer or harder than normal.[1][2]Hard to start: faults that cause it
- Rough engine running just after a cold start.[1]Vibrations: faults that cause it
- White smoke shortly after a cold start.[1]
- According to Ross-Tech, on VAG group TDIs you may not notice the pre-start glow period.[2]
- On modern cars, the glow plug light may flash or stay on when the heaters are faulty. Klavkarr warns, however, that glow plug codes P0380 and P0670 can be stored without any warning light coming on.[4][9]Flashing glow plug light: faults that cause it
How to diagnose P0671
In order: from the most likely and cheapest to check to the most expensive.
- 1Read all the codes with a diagnostic tool and note whether, alongside P0671, there are other glow plug codes (P0672 to P0674 for other cylinders, P0670 for the module or P0380). Klavkarr, discussing P0380 and P0670, points to two main culprits: a glow plug with an open circuit or the control module.[1][9]
- 2Inspect the wiring and connector of the cylinder 1 glow plug: breaks, corrosion or poor connections.[2][3]
- 3Disconnect that plug's connector or power cable and measure its resistance with a multimeter: a burnt-out glow plug reads an open circuit (infinite resistance). Klavkarr cites about 0.7 Ω on the dCi engine in his case, but warns that an ordinary multimeter is not accurate at such low values and may read 1 or 2 Ω even when there is continuity.[9]
- 4If the glow plug is fine, measure the voltage at its terminals during pre-heating: this is the test Klavkarr uses to find out whether the module is powering the glow plugs.[9]
- 5A diagnostic tool that reads all the car's modules and runs bidirectional tests identifies the failing component better than a basic reader, which only shows the code.[10]
- 6Replace the glow plug only when measurement confirms that it is open. Diariomotor warns that changing glow plugs is not always straightforward: they can snap when being removed or be firmly seized in the cylinder head, so it is best done by someone with experience.[2][4]
Can I keep driving with P0671?
Garage soon
None of the sources consulted rates the severity of this code. With just one glow plug affected, the symptoms cited by TaT and Ross-Tech are longer or harder cold starting, rough running and white smoke. Diariomotor, discussing faulty glow plugs in general, explains that the starter motor and battery suffer extra strain and that, if they fail completely, the engine refuses to start. It is best repaired before the cold weather arrives.[1][2][4]
Parts related to code P0671
The parts that most often cause this code. The code points to the circuit, not always the part: diagnose before you buy.
Battery
Alternator
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Documented faults related to P0671
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
Wiring, connectors and short circuits: the most serious faults by engine and car
- Critical severityFrequency: OccasionalBMW N62 / N63Additional turbo coolant pump with a risk of short circuit and fireIn 2011 BMW recalled 5, 6 and 7 Series, X5 and X6 models built between 2007 and 2011 because of the additional turbo coolant pump: moisture, a short circuit and, in extreme cases, a fire. In 2012 there was another campaign for a crack in the pump, with a more robust version.
- Critical severityFrequency: Occasional1.6 GDi híbrido (Kappa)Main relay of the power relay assembly (overheating and fire risk)Yes, on the first units: Hyundai and Kia recalled 2016–2018 Ioniq and Niro hybrids and plug-in hybrids because the main relay that connects the high-voltage battery could come loose, overheat and, in the worst case, cause a fire.
- Critical severityFrequency: Occasional1.6 GDi híbrido (Kappa)Clutch hydraulic actuator (HCA): leak or moisture with risk of short circuit and fireYes, this is the most documented hybrid system fault: the hydraulic actuator that engages the combustion engine with the hybrid assembly has had two recalls (2018 for a leak on the Niro and 2025 for moisture in its electronic board on the Niro, Ceed and XCeed PHEV), with a risk of short circuit and fire.
- High severityFrequency: Occasional1.3 TCeBlown fuel pump fuseOn the Renault Captur II and Clio V with the 1.3 TCe engine, a 20-amp fuse can blow and leave the car without an engine. According to L'argus, in April 2021 this fault still had no factory fix; the official service centre's diagnosis includes checking, and sometimes replacing, the catalytic converter.
- Critical severityFrequency: CommonRover 75Seat SRS connector fault with airbag and seatbelt warning light onAuto Express warns that the Rover 75's seat SRS connector can cause the airbags to fail, and dealers were fixing it with revised connectors. The Dutch APK inspection puts the airbag or seatbelt fault warning among the most frequent defects across almost all series.
- Critical severityFrequency: OccasionalAlfa Romeo GiuliettaShort circuit from badly routed wiring that can prevent gear shifting (KBA campaign, 2010-2015)Yes: according to Germany's KBA, on Alfa Romeo Giulietta cars built between 2010 and 2015 inadequate cable routing could cause a short circuit and, as a result, gear-shift failure.
12 V battery: the most serious faults by engine and car
- High severityFrequency: CommonHyundai-Kia E-GMP (Ioniq 5, Ioniq 6, EV6)Faulty ICCU: 12 V battery drains, charging fails and power is lostThe ICCU, which combines the on-board charger and the converter that powers the 12 V system, can fail on the Ioniq 5, Ioniq 6 and EV6: it cuts AC charging, drains the 12 V battery and, in the worst case, the car loses power and stops. Hyundai and Kia have recalled units built from 2021 to 2024.Repair: €2,000–€5,000
- Medium severityFrequency: Very frequent1.5 Hybrid12 V battery going flat while parkedYes: on the hybrid Yaris and Yaris Cross, the 12 V battery can go flat within a few days while parked because of the residual draw of modules such as eCall or keyless entry. It is fixed with a software update or, if the battery is already damaged, by replacing it.
- Medium severityFrequency: Very frequent1.8 HybridThe 12V battery drains on the C-HR and Corolla hybridsYes: on the first-generation C-HR hybrid, the 12V battery is one of the most frequently reported faults: it runs flat after a few days standing or on short trips, and the car will not start. The ADAC and Toyota itself point to it as a cause of faults on the C-HR and Corolla.
- Medium severityFrequency: Very frequent2.0 and 2.5 HybridThe 12 V battery goes flat if the car sits unused for several daysYes, it is a common complaint: the 12 V battery can go flat after just a few days without using the car, because of the standby drain from the electronics (multimedia, telematics, keyless entry). With the 12 V battery very low, the hybrid system can lock itself into a safe mode.
- High severityFrequency: OccasionalBMW Serie 6 E63/E64Battery drain and loose positive cableThe battery and alternator are frequently cited by Fiches-auto, and there is a recall for the battery's positive cable, which can work loose.
- High severityFrequency: OccasionalFord Galaxy IIIAcid leak from the 12 V battery (campaign 18P11)According to the fiches-auto.fr page, campaign 18P11 (August 2019) covers Galaxies built between February 2014 and February 2019 over a risk of battery acid leaking, which can worsen over time.
Alternator and starter motor: the most serious faults by engine and car
- High severityFrequency: Occasional2.2 JTDm Multijet IIAlternator cable touching the exhaust gas recirculation pipe (fire risk)An Alfa Romeo campaign covers diesel Stelvio built between 18 January 2017 and 18 September 2018: an alternator cable may rub against the exhaust gas recirculation pipe and cause a short circuit, with a fire risk in the worst case.
- Medium severityFrequency: Occasional1.7 CDTIPremature alternator wearThe Hitachi-brand alternator fitted at the factory to the 1.7 CDTI tends to wear out sooner than expected, according to a German buying guide on the Opel Astra H, with typical replacements at around 140,000 km; there are similar accounts on the Opel Meriva with this engine.
- Critical severityFrequency: OccasionalAlfa Romeo JuniorRisk of electric arcing at the 48 V starter-generator terminal on the hybrid JuniorYes: a March 2026 Safety Gate alert (campaign F60F) covers Junior MHEVs built between 27 November 2023 and 18 December 2025. The clearance between the particulate filter pipe and the 48 V starter-generator terminal cover is under 10 mm and, in damp conditions, there could be electric arcing and fire.
- Critical severityFrequency: OccasionalBMW Serie 3 G202025 campaign for corrosion of the starter motor relay (risk of fire)Yes: in September 2025 BMW recalled, among other models, the 2019 to 2021 330i (G20) because the starter motor relay can corrode, overheat and cause a short circuit with a risk of fire even when the car is parked.
Frequently asked questions
Can I drive with code P0671?
None of the sources consulted expressly forbids it, but none rates its severity either. With just one glow plug affected, what usually happens is longer cold starting, with the engine a little rough and some white smoke. Diariomotor points out that faulty glow plugs strain the starter motor and battery, and that if they fail completely the car may not start in the cold, so it is best repaired soon.[1][2][4]
What do codes P0672, P0673 and P0674 mean?
They are the same fault as P0671, but in the glow plug circuit of cylinder 2, 3 and 4 respectively. That is why they share causes and diagnosis with P0671.[5][6][7]
Does P0671 mean the cylinder 1 glow plug is broken?
Not necessarily. TaT says it is usually due to a faulty glow plug or a poor connection at that cylinder, and TroubleCodes.net adds the wiring, the relay or timer on older systems, the control module and, more rarely, the ECU. That is why the glow plug is measured and the wiring checked before it is replaced.[1][3][10]
How do you test a glow plug?
The glow plug's connector or power cable is disconnected and its resistance is measured with a multimeter: a burnt-out glow plug reads an open circuit. You can also measure the voltage at its terminals during pre-heating to see whether the circuit is powering it. Klavkarr points out that ordinary multimeters are not very accurate with such low resistances.[9]
Does code P0671 affect petrol cars?
No. TroubleCodes.net states that this code applies only to diesel engines, and Diariomotor explains that glow plugs are essential components for starting diesels.[3][4]
Will I pass the MOT with code P0671?
If the code has switched on the engine warning light, no: with that light on, the inspection records a serious defect, and on Euro 5 and Euro 6 cars the ITV (Spain's roadworthiness inspection, similar to the MOT) also reads the OBD diagnostic system. Repair the fault before you go; clearing the code just before the inspection does not help either, because it counts as a serious defect.[11]
Not sure what is wrong with your car? Describe what you notice in the symptom diagnosis or see all fault codes.
Sources
Every fact on this page links to its source. If you find an error, let us know.
- P0671 - Cylinder 1 Glow Plug Circuit/Open | Generic Fault CodeThe Automotive Technician (TaT) · Technical documentation · consulted 4 October 2026
- 17055/P0671/001649: Cylinder 1 Glow Plug Circuit (Q10): Electrical FaultRoss-Tech Wiki · Technical documentation · consulted 4 October 2026
- P0671 – Glow plug, cylinder 1 -circuit malfunctionTroubleCodes.net (BAT Auto) · Technical documentation · consulted 4 October 2026
- Cómo detectar que los calentadores de un coche diésel están en mal estadoDiariomotor · Motoring press · published 16 January 2020 · consulted 4 October 2026 · in Spanish
- P0672 - Cylinder 2 Glow Plug Circuit/Open | Generic Fault CodeThe Automotive Technician (TaT) · Technical documentation · consulted 4 October 2026
- P0673 - Cylinder 3 Glow Plug Circuit/Open | Generic Fault CodeThe Automotive Technician (TaT) · Technical documentation · consulted 4 October 2026
- P0674 - Cylinder 4 Glow Plug Circuit/Open | Generic Fault CodeThe Automotive Technician (TaT) · Technical documentation · consulted 4 October 2026
- On-board diagnosticsWikipedia · Other source · consulted 4 October 2026
- P0380 / P0670 fault codes: glow plug diagnosis and repairKlavkarr · Technical documentation · consulted 4 October 2026
- P0672 – Glow plug, cylinder 2 -circuit malfunctionTroubleCodes.net (BAT Auto) · Technical documentation · consulted 4 October 2026
- Desmontando mitos: ¿puede pasar mi coche la ITV con el testigo de «avería motor» encendido?Diariomotor · Motoring press · published 8 March 2021 · consulted 2 October 2026 · in Spanish