P0561
System Voltage Unstable
- Severity
- High
- Driving
- Drivable — book it in
The system voltage is unstable - it is moving around rather than sitting where it should. Modules read sensors by comparing them against their supply, so an unsteady supply makes steady sensors look erratic. This is one of the more useful codes to find, because it explains a great deal of otherwise baffling behaviour elsewhere in the vehicle.
Possible causes
- CommonLoose or corroded battery terminal
- CommonCorroded earth strap
- CommonFailing alternator with worn brushes or a failing regulator
- CommonSlipping drive belt
- PossibleBattery on the point of failing
- PossibleFailing diode in the alternator producing ripple
- PossibleChafed or fatigued supply wiring
What you might notice
- Lights flickering or pulsing
- Warning lights coming and going
- Erratic gauge readings
- Radio or displays resetting
- Several unrelated codes stored at once
What to check, in order
- Watch voltage on the live data screen while wiggling the battery terminals and earth straps with the engine running. A reading that jumps has located the fault.
- Check the drive belt. A belt slipping on the alternator pulley produces exactly this, and it is often audible as a squeal on a cold start or under load.
- Have the alternator tested for ripple as well as for output. A failed diode passes the output test but makes the supply unsteady.
- Perform a voltage drop test on the supply and earth circuits under load.
- Have the battery load tested. A failing battery cannot smooth the supply and produces instability that looks like an alternator fault.
- Read all stored codes but do not chase them yet. Most will disappear when the supply is stable.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Vehicle speed control, idle control and auxiliary inputs
P0500P0501P0502P0503P0504P0505P0506P0507P0508P0509P0510P0511P0512P0513P0514P0515P0516P0517P0518P0519P0520P0521P0522P0523P0524P0525P0526P0527P0528P0529P0530P0531P0532P0533P0534P0535P0536P0537P0538P0539P0540P0541P0542P0543P0544P0545P0546P0547P0548P0549P0550P0551P0552P0553P0554P0555P0556P0557P0558P0559P0560P0561P0562P0563P0564P0565P0566P0567P0568P0569P0570P0571P0572P0573P0574P0575P0576P0577P0578P0579P0580P0581P0582P0583P0584P0585P0586P0587P0588P0589P0590P0591P0592P0593P0594P0595P0596P0597P0598P0599