Electrical system and control unitsGeneric OBD-II codeUrgency: Garage soon
Code P0620: alternator control circuit fault
P0620 means: generator (alternator) control circuit.[1][2] The ECU has detected a fault in the circuit that regulates or controls the current the alternator generates. TroubleCodes.net explains that on many modern cars the alternator is governed by its own module, which may or may not be built into the engine ECU, and that current output is adjusted to what the consumers demand at any moment.[2]
What code P0620 means
The ECU has detected a fault in the circuit that regulates or controls the current the alternator generates. TroubleCodes.net explains that on many modern cars the alternator is governed by its own module, which may or may not be built into the engine ECU, and that current output is adjusted to what the consumers demand at any moment.[2]
It is a generic OBD-II code (it starts with P0), so it means the same on any brand. The sources consulted use "alternator" and "generator" as synonyms.[1][2]
Original definition (SAE J2012): Generator Control Circuit[1][2]
Causes of P0620
From most to least likely, according to the sources.
- 1Faulty alternator or a failed regulator/control module.[2][3]
- 2Wiring and connectors in the control circuit that are damaged, burnt, shorted, disconnected or corroded.[2][3]
- 3Faulty battery or voltage spikes from a badly done jump start, which can damage the control units.[2]
- 4Fuse or relay problems, or a worn alternator belt.[3]
- 5Fault in the engine ECU or another module, which TroubleCodes.net calls rare and which should only be suspected after ruling out everything else.[2][3]
Symptoms
- Warning light or battery warning on the dashboard.[2][3]Engine warning light: faults that cause it
- Charging system voltage that is abnormally high or low, or fluctuating.[2][3]Charging failure: faults that cause it
- Battery discharged or damaged by the incorrect voltage.[2]Battery goes flat: faults that cause it
- Difficulty starting or inability to start.[2][3]Hard to start: faults that cause it
- Instrument cluster gauges that "freeze" or failures of other electrical systems.[2][3]Electronic warnings: faults that cause it
How to diagnose P0620
In order: from the most likely and cheapest to check to the most expensive.
- 1Note all the codes present: this fault can trigger many others, which are usually a consequence and not the cause.[2]
- 2Measure the battery voltage with the engine off and running to check whether the alternator is charging, and check the condition of the battery itself.[2]
- 3Visually inspect the wiring, connectors, earths, fuses and relays of the charging circuit and the alternator belt.[2][3]
- 4If all of this is fine, check the alternator's regulator or control module and, only at the end, the ECU. TroubleCodes.net recommends going to a garage with professional equipment, because the diagnosis involves the CAN network.[2][3]
Can I keep driving with P0620?
Garage soon
AutoDTCs classifies it as moderate severity ("fix soon, normally won't leave you stranded"). Even so, if the alternator is not charging, the car runs on the battery alone and may stop; TroubleCodes.net adds that a voltage that is too high or too low can damage the battery and the control units.[2][4]
Parts related to code P0620
The parts that most often cause this code. The code points to the circuit, not always the part: diagnose before you buy.
Alternator
Battery
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Documented faults related to P0620
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
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.
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.
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.
Frequently asked questions
Can I drive with code P0620?
You should take it to a garage as soon as possible. If the alternator is not charging, the car lives off the battery and ends up stopping, and abnormal voltage can damage the battery and the control units.[2][4]
Does P0620 mean the alternator is broken?
Not necessarily. The code points to the control circuit: it could be the alternator, its regulator, the wiring, a fuse or relay, the battery or, more rarely, a control unit.[2][3]
What other symptoms go with P0620?
The sources cite a warning light on, unstable voltage, hard starting, gauges that stay fixed and assorted electrical faults; the extent depends on the model.[2][3]
Will I pass the MOT with code P0620?
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.[5]
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.
- P0620 DTCDTCSearch · Technical documentation · consulted 29 October 2026
- P0620 trouble codeTroubleCodes.net · Technical documentation · consulted 29 October 2026
- OBD Fehlercode P0620CarWiki · Technical documentation · consulted 29 October 2026 · in German
- P0620 diagnostic trouble codeAutoDTCs · Technical documentation · consulted 29 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