P0563 System Voltage High on Smart Fortwo 451 / 453
P0563 is system voltage high. On a Smart this is usually a regulator-side alternator fault — the alternator is overcharging. Check charging voltage at idle and at 2000 rpm before swapping the alternator.
Typical Symptoms
- Check engine light with code P0563
- Charging voltage above 14.6V at the battery
- Battery getting hot or smelling sulfurous
- Headlights or interior lights brighter than usual
- Light bulbs failing repeatedly
- Battery boiling electrolyte (vented battery only)
What it means
P0563 is the opposite of P0562. The ECU is seeing system voltage above the threshold it expects with the engine running — usually 14.6 volts or more. A normal charging system sits between 13.8 and 14.4 volts at the battery posts. When that climbs, the cause is almost always the voltage regulator on the alternator, which has stopped clamping output where it should.
On a Smart this is less common than P0562 but more damaging if you ignore it. Sustained overcharging cooks the battery, kills bulbs faster than normal, and can take out other electronics if it gets bad enough. The diagnostic path is short: measure charging voltage with a multimeter and confirm where it actually sits before you replace anything.
Likely causes, cheapest first
- Alternator regulator failed. The dominant cause. The regulator has stopped limiting output and the alternator is putting whatever it can produce onto the bus. Fix is alternator replacement on most modern setups, since the regulator is integrated.
- Wiring or connector fault at the alternator sense lead. Less common, but worth a quick look. The alternator uses a sense lead to know what voltage it's actually producing at the battery — if that lead is broken, the regulator overshoots trying to compensate.
- Bad ground at the alternator or engine. A poor ground confuses the regulator about real system voltage and it overcharges to compensate.
DIY check steps
- Measure charging voltage at idle. Engine running, no accessories on, multimeter on the battery posts. Healthy is 13.8 to 14.4 volts. Above 14.6V at idle is the textbook P0563 reading.
- Measure charging voltage at 2000 rpm. Same setup, hold the throttle steady. The number shouldn't climb much — still in the 13.8 to 14.4 range. A number that pegs above 15V on revs is a regulator that's lost control.
- Check the alternator sense lead and main charging cable. Visual inspect for chafe, loose terminals, or corroded ring connectors at the alternator and the battery.
- Inspect the engine and chassis grounds for corrosion or looseness.
- Don't keep driving it. If charging voltage is well above 15V, every minute is shortening the battery's life and stressing every electronic module on the car. Park it until you can fix it.
When to call a shop
If voltage is confirmed too high and the wiring and grounds check out, the alternator is the answer. Replacement is a job most owners can DIY on a Smart, but if the car is running hot voltage and you don't want to risk frying other modules in the meantime, a Smart-experienced shop can swap the alternator and confirm output in well under a half-day. Have the battery load-tested at the same time — a battery that's been overcharged for a while is often already on borrowed time.
Related parts & typical prices
| Part | Typical price | Search |
|---|---|---|
| Alternator (rebuilt) | $150-350 | Search Google |
| Voltage regulator (if separately serviceable) | $40-120 | Search Google |
| Battery (replace if it's been cooked) | $100-180 | Search Google |
Prices are rough community-reported ranges, not quotes. Aftermarket vs. genuine Mercedes parts swing the spread; call a Smart-experienced shop for an actual quote.
Manual references
- Service manual on Manualslib — external mirror (we don't host this specific document).
- Browse Smart manuals on smartcarmanuals.com — pick your chassis code section on the home page if a specific manual isn't listed above.
Community references
Stuck on this one?
SmartDiag-AI runs through the cheap-first checks with you, weighted to community-known patterns for your exact model. The link below pre-fills the code and model.