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P0563 on 2011-2018 Subaru Forester: High Voltage Causes and Alternator Fix

On a 2011-2018 Subaru Forester, the P0563 code almost always means the alternator's internal voltage regulator has failed, causing a dangerous high-voltage condition. The only fix is to replace the entire alternator assembly. Expect to pay $500-$750 for an OEM part and $180-$400 for a quality aftermarket replacement.

18 minutes to read 2011-2018 Subaru Forester

Most Likely Cause

Failing Alternator (Internal Voltage Regulator)

Difficulty

2/5

Est. Time

1.5 hrs

DIY Doable?

✅ Yes

Shop Labor

$350 – $1200

Parts Price

$187 – $750

⚠️ Drivable, but... — It is recommended to limit driving. A sustained high-voltage condition can damage the battery, the PCM, and other expensive electronic modules throughout the vehicle. Overcharging can boil the battery acid and cause irreparable damage to sensitive electronics.

Key Takeaways

P0563 on your Forester means the system voltage is too high, and the alternator is almost certainly the cause.
Confirm the failure by checking the voltage at the battery with the engine running. A reading over 15.0V means the alternator is bad.
Do not replace the battery first; it is a victim of the overcharging alternator, not the cause of the problem.
Replacing the alternator is a DIY-friendly job that can be completed in 1-2 hours with basic hand tools.
Driving with this condition is risky and can lead to costly damage to other electronic components.

The trouble code P0563 stands for "System Voltage High." This means the vehicle's Powertrain Control Module (PCM) has detected that the electrical system's voltage is dangerously above the normal operating range. A healthy charging system on a running Forester should maintain a voltage between 13.2 and 14.8 volts. This code is triggered when the voltage consistently exceeds this limit, often spiking to 15.5, 16.0, or even 17.0+ volts for a set period. Some vehicle systems will set the code when voltage exceeds 16V.

What's Unique About the 2011-2018 Subaru Forester

For this generation of Subaru Forester, the P0563 code is a definitive indicator of a failed alternator. Unlike some vehicles where this code could have multiple complex causes, on the Forester with the FB25B engine, the root cause is almost invariably the internal, non-serviceable voltage regulator. This simplifies diagnosis significantly, as other potential causes like wiring or PCM issues are very rare. The alternator's output is not heavily controlled by the PCM via pulse-width modulation on this platform, making it a more straightforward hardware failure.

Generation note: This range covers two Forester generations: the third generation (SH, 2011-2013) and the fourth generation (SJ, 2014-2018). Both generations use the FB25B 2.5L engine and share the same common cause for P0563. A key difference is that the 2011-2013 models have hydraulic power steering, while the 2014-2018 models switched to electric power steering, which does not affect this specific fault.

Symptoms You May Notice

Check Engine Light is on
Battery or charging system warning light is on
Headlights and interior lights are unusually bright, flickering, or burning out prematurely
Erratic behavior from electronic accessories like the radio or power windows
Engine may hesitate, stall, or run rough
Battery feels hot to the touch or appears swollen
A noticeable burning smell from the alternator or battery due to overheating

🎬 See what a failing alternator sounds and smells like

⚠️ Don't Waste Money on the Wrong Fix

Replacing the battery. The battery is almost always the victim of the overcharging condition, not the cause. A high-voltage situation can damage a good battery, but a bad battery will not cause a P0563 code.

Most Likely Causes

Failing Alternator (Internal Voltage Regulator) 🔴 High Probability The internal voltage regulator is a known failure point on alternators used in this generation of Subaru vehicles, leading to an overcharging condition. This accounts for over 90% of P0563 cases on this platform.
How to confirm: With the engine running, use a multimeter to measure the DC voltage directly across the positive and negative battery terminals. A consistent reading above 15.0 volts confirms the alternator is overcharging and has failed.
Typical fix: Replace the entire alternator assembly. 🎬 Watch: Step-by-step Subaru alternator replacement guide The voltage regulator is internal and not sold as a separate, serviceable component.
Est. part cost: $180 - $750

Rare But Worth Checking

Poor Ground Connection: A loose or corroded ground strap for the engine, battery, or PCM can create resistance and cause erratic voltage readings. Always inspect main ground points before replacing parts. Key grounds are from the negative battery terminal to the chassis and from the engine block to the frame rails.
Wiring or Connector Faults: Corroded battery terminals or a damaged wire between the alternator and the battery can cause voltage regulation issues. A fault in the 'S' (Sense) wire circuit at the alternator's 3-pin connector can also cause it to overcharge. This is worth inspecting, especially if a new alternator does not fix the code.
Faulty Powertrain Control Module (PCM): In extremely rare cases, the PCM's internal voltage monitoring circuit can fail, causing it to misread the system voltage. This should only be considered after all other possibilities have been exhausted.

Diagnosis Steps

Confirm the P0563 code is present using an OBD-II scanner.
With the engine running, use a multimeter set to DC volts to measure the voltage across the battery terminals.
If the voltage is consistently above 15.0V, the alternator has failed and needs to be replaced.
If the voltage is normal (13.2V-14.8V), turn on all electrical accessories (headlights, blower fan, rear defroster) and re-check. Voltage spikes may indicate an intermittent failure.
If voltage remains normal, inspect the battery terminals for corrosion and tightness. Follow the main battery ground cable and engine ground straps to ensure they are clean, tight, and free of corrosion.
Inspect the main power wire and electrical connector at the alternator for any signs of damage or corrosion.
As an advanced check, set the multimeter to AC volts and measure at the alternator's B+ terminal (with the engine running). A reading higher than 0.4V AC indicates failing diodes inside the alternator, which requires replacement.
If all wiring and grounds are good and the voltage test was inconclusive, the alternator may be failing intermittently. However, given the high probability of alternator failure with this code, replacement is the most likely next step.

Parts You'll Likely Need

Alternator (OEM #23700AB030 (for 2014-2016 models, per TSB 07-112-16R), 23700AA871 (supersedes 23700AA870, 23700AA681, 23700AA680 for some applications). Always verify with VIN.) — This is the direct cause of the P0563 code in over 90% of cases on this vehicle due to internal voltage regulator failure.
Trusted brands: Subaru (OEM), Denso (often the OEM supplier), Bosch, TYC
OEM price range: $590 - $750
Aftermarket price range: $187 - $400

Technical Service Bulletins (TSBs) & Recalls

07-112-16R

Platform-Specific Known Issues

A faulty alternator on 2014-2016 Foresters is known to cause electrical noise that can trigger a 'phantom' P0300 (Random Misfire) code. Subaru issued TSB 07-112-16R for this issue, which requires an updated alternator (Part No. 23700AB030) and belt tensioner. The updated alternator can be identified by its silver pulley surface, whereas the original, problematic one has a black pulley.

🎬 Watch: How a bad alternator triggers a P0300 misfire

Mechanic-Grade Diagnostic Values

Battery Voltage (Key-On-Engine-Off) — expected: 12.4V - 12.7V DC. Failure: A reading below 12.4V indicates a discharged or failing battery, which should be charged and tested independently before diagnosing the charging system.
Charging Voltage at Battery Terminals (Engine Idling, No Load) — expected: 13.2V - 14.8V DC. Failure: A consistent reading above 15.0V, often spiking to 16.0V or higher, confirms an overcharging condition caused by a faulty internal voltage regulator.
Charging Voltage at Battery Terminals (Engine Idling, Full Load) — expected: Voltage should remain stable within the 13.2V - 14.8V range, possibly dipping slightly but not below 13.0V.. Failure: Wild fluctuations or a significant spike above 15.0V when accessories like headlights, A/C, and rear defrost are turned on indicates a failing voltage regulator.
AC Voltage Leakage at Alternator B+ Post — expected: Less than 0.4V AC. Failure: A reading higher than 0.4V AC indicates failing diodes within the alternator, which requires replacement of the unit.

Wiring & Ground Locations

Alternator 3-Pin Connector — Plugged into the side of the alternator housing.. This connector contains the 'S' (Sense) and 'L' (Lamp) wires. The 'S' wire is the voltage sense wire the regulator uses to determine how much current to supply. A poor connection or break in this circuit can cause the alternator to regulate voltage incorrectly. The 'L' wire controls the battery warning light on the dash. Some newer Subarus may also have a 'C' (Computer) terminal for ECU control, though this is less critical for the P0563 fault on this platform.
GE (Engine Ground) — Main ground strap from the engine block to the chassis/frame rail.. The alternator grounds through its metal case to the engine block. A poor engine ground connection adds resistance to the charging circuit, which can cause erratic alternator behavior and voltage regulation problems.
GB (Body Ground) — Main ground cable from the negative battery terminal to the vehicle's chassis, typically on the strut tower or inner fender.. This is the primary ground for the entire vehicle's electrical system. Corrosion or a loose connection here can cause widespread electrical issues, including incorrect voltage readings by the PCM.
Main Fuse Box — Located in the engine bay, near the battery on the driver's side.. The main power cable from the alternator's B+ post connects to the fuse box. A loose or corroded connection at this point can cause high resistance and charging system problems.

Real Owner Repair Stories

subaruforester.org forum user (2011 Subaru Forester) — Battery light came on, multimeter showed voltage spiking to 17.2V.
❌ Tried (didn't work) Initially considered replacing the battery but tested the charging system first.
✅ What actually fixed it Replaced the original alternator with a new TYC brand alternator. After replacement, the voltage stabilized at a normal 14.4V and the P0563 code was resolved.

OEM Part Supersession History

23700AA680, 23700AA681, 23700AA870 → 23700AA871 — Standard part evolution for improved reliability or manufacturing changes.
Heads up: These part numbers are generally for the non-turbo FB25B engine and are cross-compatible. However, always verify the correct part number with the vehicle's VIN.

Model Year Variations Within This Range

2014-2016: These model years are specifically mentioned in TSB 07-112-16R regarding an alternator that produces electrical noise, potentially triggering a P0300 misfire code alongside charging issues. The updated alternator (23700AB030) has a silver pulley, distinguishing it from the problematic original with a black pulley.

Diagnostic Flowchart

Start by confirming the P0563 (System Voltage High) code and checking for accompanying symptoms like flickering lights or 'phantom' misfire codes common on the FB25B engine.

Inspect the alternator pulley. Is the pulley surface black or silver?

→ The black pulley indicates the original problematic alternator. Per TSB 07-112-16R, electrical noise is likely causing the P0563 and phantom P0300. Replace with updated Alternator (Part No. 23700AB030) and new belt tensioner.

With the engine running, measure DC voltage across the battery terminals. Is the reading consistently above 15.0V?

→ The internal voltage regulator has failed. On the FB25B, this is a high-probability failure (90%+ of cases). Replace the entire alternator assembly as the regulator is not serviceable separately.

Turn on headlights, blower fan, and rear defroster. Does the voltage spike above 15.0V or fluctuate wildly?

→ The alternator is failing intermittently. Given the platform's history of regulator failure, replace the alternator assembly now to prevent damage to the battery or electronic accessories.

Set multimeter to AC volts. Measure at the alternator B+ terminal with the engine running. Is the reading higher than 0.4V AC?

→ Internal diodes have failed, allowing AC ripple into the DC system. This causes the P0563 and erratic accessory behavior. Replace the alternator.

Inspect the main battery ground cable, engine ground straps, and the alternator connector. Are they clean and tight?

→ Clean all ground points and the alternator B+ terminal. Ensure the harness connector is fully seated. Clear codes and retest.

→ If voltage tests were inconclusive but symptoms like 'burning smell' or 'swollen battery' persist, the alternator is likely failing intermittently. Replace the alternator as a preventative measure due to known FB25B charging system weaknesses.