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Home / DTC / P0563 — System Voltage High

P0563 — System Voltage High

Detailed page for trouble code P0563.

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Code

P0563

MERCEDES-BENZ P — Powertrain

System Voltage High

Brand: MERCEDES-BENZ
Type: P — Powertrain
AI status
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Page language: EN

Causes

  • Faulty alternator voltage regulator (internal to alternator)
  • Stuck or shorted alternator field/control circuit
  • Shorted wiring or a short to battery positive (B+) feeding control module power rail
  • Faulty battery positive voltage sensor or incorrect sensor reading
  • Aftermarket charger, inverter, jump-starter, or improper charging device connected
  • Faulty PCM/ECM or voltage sensing circuit

Symptoms

  • Battery/charging system warning lamp illuminated
  • Electrical accessories unusually bright or overactive (lights, HVAC blower)
  • Intermittent or permanent stored P0563 code(s) and possible limp-home strategy
  • Blown fuses or damaged electronic modules if over-voltage sustained
  • Unusual ECU or instrument cluster behavior (restarts, error messages)

What to check

  • Read and record freeze-frame and live data from BCM/ECM — note battery voltage (key ON, engine OFF; engine running idle; at higher rpm)
  • Visually inspect battery terminals, positive cable, and ground connections for corrosion, looseness or damage
  • Inspect wiring and connectors between alternator and battery/ECM for damage, heat, or chafing
  • Check for recent aftermarket charging devices, inverters, jump-starters or battery chargers attached
  • Confirm vehicle electrical architecture (12V vs 48V hybrid) and follow high-voltage safety if applicable
  • Scan for related codes (alternator/generator control, battery sensor, CAN/communication faults)

Signal parameters

  • Battery resting voltage (key OFF): ~12.4–12.8 V (typical, varies by battery state-of-charge)
  • Charging voltage (engine running, no load): normally ~13.5–14.8 V
  • Charging voltage under load should remain in manufacturer specified range; sustained voltage >16.0 V is commonly considered an over-voltage condition (thresholds vary by manufacturer)
  • Voltage sensor/ECM reference voltages will vary by model — compare measured values to OEM data

Diagnostic algorithm

  1. Verify and record DTCs and freeze-frame data with a diagnostic scan tool; note voltage at time code set
  2. Confirm vehicle electrical system type (12V/48V) and use appropriate safety procedures
  3. With ignition ON (engine OFF), measure and record battery voltage at battery positive and at ECU/BCM power input; repeat with engine running at idle and at ~2000 rpm
  4. Inspect battery terminals and grounds; clean and tighten connections; re-check voltages
  5. Visually inspect alternator wiring, connectors, and harness for shorts to B+ or damage; repair as needed
  6. Test alternator output with a multimeter: check voltage at battery with engine running. If voltage is above expected range, isolate alternator by disconnecting its regulator/field connector (follow OEM procedure) and re-measure system voltage
  7. If disconnecting alternator removes the over-voltage condition, suspect internal regulator or diode failure in alternator — bench test or replace alternator
  8. If over-voltage remains with alternator disconnected, inspect battery positive sensor, power distribution, fuses, relays and ECM power supply circuits; check for shorted aftermarket equipment connected to B+
  9. Check grounds and negative return paths for high resistance; repair as required and re-test
  10. If wiring and charging unit test good, test or replace voltage sensing module/ECM as last resort per OEM procedures
  11. After repairs clear codes and road-test; verify live voltage values and that P0563 does not return

Likely causes

  • Internal alternator/regulator failure causing uncontrolled charging voltage
  • Shorted alternator field/control wire to battery +
  • Failed battery positive voltage sensor or open/short in its circuit
  • Aftermarket charger/inverter connected or recently used jump-starting with incorrect polarity/connection
  • Loose/corroded ground or battery terminals causing unstable voltage readings

Fault status

⚠️ Status
Control module detected vehicle electrical system voltage higher than allowable threshold. This may cause control modules to log a fault and illuminate warnings. Continued over-voltage can damage electrical components; diagnostic checks of the charging system, wiring and voltage-sensing circuits are required.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

Similar codes

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856

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