Ignition and pre-heatingGeneric OBD-II codeUrgency: Garage soon
Code P0670: glow plug control module circuit
P0670 means: glow plug control module circuit: malfunction.[1][2][3][4][5] The ECU has detected a fault in the glow plug control module circuit. This is the unit that powers the glow plugs of a diesel engine before and after starting. According to BorgWarner, the module sets the timing, intensity and duration of the current the glow plugs receive and, in current systems, keeps up constant communication with the engine ECU; in older ones it works mostly as a switch. Autodoc Club says the code mainly affects diesel cars.[1][2][6]
What code P0670 means
The ECU has detected a fault in the glow plug control module circuit. This is the unit that powers the glow plugs of a diesel engine before and after starting. According to BorgWarner, the module sets the timing, intensity and duration of the current the glow plugs receive and, in current systems, keeps up constant communication with the engine ECU; in older ones it works mostly as a switch. Autodoc Club says the code mainly affects diesel cars.[1][2][6]
The code points to the module circuit, not to a specific part. According to the sources, the fault may be in the module itself, in its power supply and earth, in the wiring and connectors, or in the lines linking it to the ECU. In the workshop manual for the diesel Saab 9-5, for example, the code is detected by comparing the module's diagnostic line with the line that activates it, and a distinction is made between open circuit, short to positive and short to earth.[3][5][7]
Klavkarr distinguishes it from P0380: P0380 refers to the glow plug circuit ("A") and P0670 to the control module; neither of them identifies the exact cause on its own. Klavkarr also documents a case in which P0670 was stored without the engine warning light coming on, whereas the Saab manual and other sources cite it with the light on.[2][3][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): Glow Plug Control Module Circuit Malfunction[1][2][3][4][5]
Causes of P0670
From most to least likely, according to the sources.
- 1Faulty glow plug control module (preheating unit).[1][2][3][5][7]
- 2Wiring and connectors in poor condition: damaged, burnt or shorted wires, corroded or loose connectors, bent terminals.[1][3][5][7]
- 3Faulty glow plugs. Klavkarr, in its example with a Renault/Nissan dCi engine, names them as the most likely cause.[2][3][5][7]
- 4Blown fuse (or high-current fuse) in the glow plug circuit.[1][3][5]
- 5Faulty, loose or corroded earth on the control unit.[1][5]
- 6Faulty glow plug relay.[1][2]
- 7Faulty engine (coolant) temperature sensor.[3][5]
- 8Cited by a single source or uncommon: faulty starter switch and engine ECU failure.[1][3]
Symptoms
- Hard starting, or starting that takes longer than normal, getting worse in the cold.[1][3][5]Hard to start: faults that cause it
- Abnormal glow plug warning light (flashes, takes a long time to go out or stays on), often together with the engine warning light.[5][9]Flashing glow plug light: faults that cause it
- Engine warning light on, although Klavkarr warns that the code can be stored without any warning light coming on.[2][3][5][7]Engine warning light: faults that cause it
- White smoke from the exhaust on a cold start.[1][3]
- Uneven running while the engine warms up.[1][5]Vibrations: faults that cause it
- Loss of power and hesitation, especially with a cold engine.[1][3][5]Less power: faults that cause it
- Increased fuel consumption.[3][5]Uses more fuel: faults that cause it
How to diagnose P0670
In order: from the most likely and cheapest to check to the most expensive.
- 1Confirm the code with a diagnostic tool and check for other glow plug codes: P0380 and the ones for each individual plug, which TaT groups between P0671 and P0675. Also check that the battery is well charged.[2][4][5]
- 2Check the high-current fuse and the relay of the glow plug circuit: it is the quickest and cheapest thing to check.[1][5]
- 3Check the earths and use a multimeter to measure the supply and earth at the module connector.[1][5]
- 4Check the module's output to the glow plugs: during preheating, measure the voltage at the glow plug terminals.[2][5]
- 5Inspect the wiring and connectors between the ECU, the module and the glow plugs (corrosion, bent terminals, moisture) and check their continuity against the wiring diagram.[1][3][7]
- 6Measure each glow plug separately: a burnt-out plug reads as an open circuit (infinite resistance). Klavkarr quotes about 0.7 Ω on a dCi engine, but the value depends on the engine. FleetRabbit leaves this step until last.[2][5]
- 7Replace the module only after a professional diagnosis confirms it, and the engine ECU only if everything else is fine.[1]
- 8Clear the code after the repair and check that it does not come back. In the diesel Saab 9-5 manual, if a P0380 or a P1380 also appears, they are ignored while P0670 is being diagnosed.[2][7]
Can I keep driving with P0670?
Garage soon
No source says to stop driving the car. Autodoc Club says you can drive for a short time, but that the code should be repaired as soon as possible. FleetRabbit explains that in mild weather the vehicle usually starts and runs, with hard cold starts as the visible symptom, but that wear on the starter motor and battery and higher fuel consumption build up unnoticed, and that the first cold snap sets the limit. Diariomotor, speaking about faulty glow plugs in general, adds that the starter motor and battery come under extra strain and that the car may fail to start if the fault is total. Klavkarr warns that the code can be stored without any warning light coming on.[1][2][5][9]
Documented faults related to P0670
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.
- 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.
- High severityFrequency: OccasionalM264/M254Poorly tightened 48 V earth wiring in the mild-hybrid system (fire risk)Mercedes-Benz has issued several recalls (2022-2025) because the 12 V and 48 V earth connections of some cars with a 48 V system may be poorly tightened: resistance rises, the connection heats up and a fire cannot be ruled out. The official workshop checks them and repairs them if necessary in an hour or more.
- High severityFrequency: Occasional1.9 TDIUnit injector tappet wear and injector wiring damageOn the unit injector system, the tappets that operate the injectors can wear if the oil is not changed on time, and the injector wiring can be damaged by contact with oil, causing misfires or loss of power.
- 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.
Control units and comfort electronics (BSI, SAM...): the most serious faults by engine and car
- High severityFrequency: CommonPeugeot 408Electronic faults with the doors, boot and screen (suspected BSI control unit)In 2025 Peugeot recalled around 60,000 2023-2024 Peugeot 308 and 408 cars (code MUV) over a software fault in the door control unit that can cause unintended opening or closing and disable the anti-trap protection on the windows; 408 owners also describe a power boot lid that will not open or close and a screen that goes black.
- High severityFrequency: CommonRenault Laguna IIMultiplex electrical system and hands-free card faultsThe Laguna II had a reputation problem because of faults in its multiplexed electrical network: the hands-free card, the card reader and the ABS, ESP and handbrake warning lights came on erratically, especially in the early years of production (2001-2003).
- Critical severityFrequency: OccasionalMazda MX-5 IVDC/DC converter control unit fault with risk of short circuit and fireA 2018 Safety Gate alert covers MX-5 ND models built between August 2014 and April 2017: the DC converter control unit could fail, cause a short circuit and damage the converter, with a risk of fire. It is a precautionary recall; check the chassis number at the official service centre.
- Medium severityFrequency: Very frequentFiat StiloElectrical and electronic faults in the multiplex systemThe Stilo has had a reputation for widespread electrical faults since its launch: poor contacts in the multiplex wiring, an instrument cluster that switches off and sensors that disconnect, sometimes while the car is running.
12 V battery: the most serious faults by engine and car
- Medium severityFrequency: Common2.0 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.
- Medium severityFrequency: OccasionalE-Tech Híbrido12 V battery going flat or needing early replacementSeveral Clio, Arkana and Austral owners with the E-Tech engine document premature replacement of the 12 V auxiliary battery, in one case twice in the first year. It is not the most widespread fault of the system, but it appears repeatedly across different models.
- Medium severityFrequency: Occasional1.5 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.
- Low severityFrequency: OccasionalHonda e:HEV / i-MMD12 V battery going flat and hybrid system failing to startIf the car stands unused for a long time, the 12 V auxiliary battery can go flat and the hybrid system does not activate ("Ready" does not appear) even though the traction battery is charged. It is fixed by charging or replacing the battery.Repair (garage): €120–€250
- High severityFrequency: CommonHyundai Ioniq 5Faulty ICCU: 12 V battery drain and loss of drive powerThe Integrated Charging Control Unit (ICCU) can fail on the Ioniq 5: it drains the 12 V battery, may refuse to charge and, in the most serious cases, cause the car to lose power or not go into drive mode. Hyundai has replaced this part and updated its software on units built between January and February 2023.
- 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.
Frequently asked questions
What is the difference between P0670 and P0380?
Both affect the preheating of a diesel engine and neither identifies the exact cause on its own, but they point to different parts. According to Klavkarr, P0380 refers to the circuit of glow plug "A" and P0670 to the control module that powers them; it illustrates them with different engines (P0670 with a Renault/Nissan dCi and P0380 with a Peugeot 306 2.0 HDi), so which of the two appears also depends on each manufacturer's system. TaT also lists codes of their own for each individual plug (P0671 to P0675). That is why, with P0670, you start with the fuse, the earths, the supply and the module's output, and the plugs are measured last, as FleetRabbit prescribes.[1][2][4][5]
Can I drive with code P0670?
Yes, in the short term: Autodoc Club allows it, but asks for it to be repaired as soon as possible. FleetRabbit adds that in mild weather the car usually starts and runs, but that wear on the starter motor and battery builds up without warning and that the first cold snap sets how long the repair can be put off. No source says to stop driving the car, but it is best to take it to a garage soon.[1][5][9]
Does code P0670 mean the glow plugs are broken?
Not necessarily. The code points to the control module circuit, and the cause may lie in the module, the fuse, the relay, an earth, the wiring or the connectors. Klavkarr recommends measuring each glow plug and, if they are fine, suspecting the module or its relay; FleetRabbit leaves the glow plugs for the last step.[1][2][3][5]
Does P0670 always turn on the engine warning light?
There is no agreement. Klavkarr documents a case in which the code was stored without any warning light coming on, whereas the Saab 9-5 diesel manual states that the engine warning light comes on and FleetRabbit cites a glow plug light of its own alongside the engine warning light. That is why it is worth reading the codes even when no warning lights are on.[2][5][7]
Does P0670 affect petrol cars?
In principle no. Autodoc Club says it mainly affects diesel cars, and Diariomotor explains that glow plugs heat the combustion chamber of diesels before starting so that the mixture ignites by compression.[1][9]
What does the glow plug control module do?
It manages the current the glow plugs receive during the preheating before starting and the post-heating once the engine is running. According to BorgWarner, it sets the timing, intensity and duration of that current and, in current systems, communicates constantly with the engine ECU; Klavkarr adds that it powers the glow plugs in the preheating and post-heating phases.[2][6]
Will I pass the MOT with code P0670?
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.[10]
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.
- Código OBD2 P0670: causas, síntomas y cómo corregirloAutodoc Club · Technical documentation · consulted 2 October 2026 · in Spanish
- P0380 / P0670 fault codes: glow plug diagnosis and repairKlavkarr · Technical documentation · consulted 2 October 2026
- Error Code P0670: What It Means & What To Do?PartsAvatar · Technical documentation · published 2022 · consulted 2 October 2026
- P0670 — Glow plug control module circuit openThe Automotive Technician (TaT) · Technical documentation · consulted 2 October 2026
- P0670 Code: Glow Plug Control Module FaultFleetRabbit · Other source · published 3 September 2026 · consulted 2 October 2026
- Glow Plug Control UnitsBorgWarner Aftermarket · Manufacturer · consulted 2 October 2026
- P0670 (9-5 9600, 2004, PSG 16 D223L): códigos de averíaSaab WIS Online (Saab Workshop Information System) · Technical documentation · consulted 2 October 2026
- On-board diagnosticsWikipedia · Other source · consulted 2 October 2026
- Cómo detectar que los calentadores de un coche diésel están en mal estadoDiariomotor · Motoring press · published 16 January 2020 · consulted 2 October 2026 · in Spanish
- 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