Fix P0563: Mechanic’s solutions that WORKED

The OBD2 code P0563 is triggered when the vehicle’s onboard computer detects that the system voltage is excessively high, typically above the manufacturer’s specified range. This can affect the vehicle’s electrical systems and, if not addressed, may lead to more serious issues. It’s a signal that the charging system is working outside its normal parameters, which can cause various electrical components to malfunction.

P0563 quick overview

Meaning	P0563: System Voltage High
Is it serious?	Yes, this code indicates a potential overcharging issue which can damage electrical components and the battery.
Possible causes	– Faulty alternator or voltage regulator – Poor battery condition – Wiring issues (shorts, open circuits, poor connections) – Faulty Powertrain Control Module (PCM)
How to diagnose?	Check the battery condition and voltage. Inspect the alternator and charging system output. Examine electrical connections for corrosion or damage. Review the vehicle’s ground connections and wiring harness. Test the PCM for proper operation and output.

How to fix P0563 – learn from mechanics

I looked into P0563 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: GMC

Vehicle Information:
1999 GMC Sierra 2500 SL 6.0L

Issue + Repair History:

• Customer complaint of low power transmission and won’t shift.
• Test drive revealed low power and low fuel pressure.
• Fuel pressure initially at 45 psi, replaced fuel pump, pressure at 60 psi.
• Checked alternator voltage, 12.5 volts low, checked at ECM the same.
• Wiring checked okay, no shorts or grounds.
• Code P0563 sets even with engine not running.
• Back pressure minimal.
• Replaced PCM and reprogrammed to vehicle, cured all problems.

Other OBD2 Codes + Test Results:

• OBD2 Code: P0563 – PCM overvoltage
• New fuel pump: 60psi
• Low or no injector drive: Cylinder 1-3-5-7

Mechanic Suggestions:

• Suspected PCM issue mentioned by multiple technicians.
• Suggested checking battery and ignition voltage.
• Alternator regulator also suspected by one technician.
• Mention of potential ECM issue that shorted out, suggesting reprogramming at a GM dealer.
• Suggestion for acquiring a scan tool for future diagnostics.

Final Fix:

• Replacing the PCM and reprogramming it to the vehicle resolved all issues.

Case #2: Chrysler

Vehicle Information:
2005 Chrysler 300 Touring 3.5L

Issue + Repair History:

• Vehicle intermittently sets a P0563 battery volts high.
• Battery light and check engine light come on intermittently.
• Alternator and wire from alternator to PCM have been replaced.
• TSB not available for the problem.
• Battery volts stay around 13.25 – 13.45 regardless of RPMs or loads.

Other OBD2 Codes + Test Results:

• OBD2 Code: P0563 – Battery volts high
• Charging system test (with Snap-on DTAC): Good
• Charging volts: 13.25-13.45

Mechanic Suggestions:

• Replace alternator with OEM alternator and replace battery.
• Test for battery temperature and alternator plug connection.
• Check vehicle sales codes for potential emissions-related issues.
• Consider trying a new battery.
• Inspect battery positive connection and wires to the alternator for corrosion.
• Ensure correct battery size and good grounds to engine, computer, and alternator.

Final Fix:

• Replaced alternator with OEM unit and replaced the battery.

Case #3: Cadillac

Vehicle Information:
2002 Cadillac Seville SLS 4.6L

Issue + Repair History:

• Car brought in with battery lamp on, codes P0621 and P0563 stored and reset when cleared.
• Charging voltage is 14.5 volts at battery and ignition one terminals.
• Tech 2 shows L terminal always off.
• Suspected short in alternator by one technician, another technician suspects PCM.
• Battery is in good shape.

Other OBD2 Codes + Test Results:

• OBD2 Codes: P0621, P0563
• Charging system check: Reading 14.4 volts at battery and ignition one terminal.

Mechanic Suggestions:

• Confirm alternator is capable of putting out at least 5 amps more than the vehicle draws with all its options turned on.
• Consider replacing the alternator as it may be the source of the problem.
• Check the condition of the belt and tensioner, and try a different alternator if necessary.

Final Fix:

• Replaced alternator with a new AC Delco unit, which resolved the issue.

Diagnostic Step	Brief Explanation
Check battery condition and voltage	Ensure the battery is in good condition and not overcharging.
Inspect alternator output	Verify that the alternator is not sending too much voltage.
Examine electrical connections	Look for any signs of corrosion, damage, or poor connections.
Review ground connections and wiring	Ensure all grounds are secure and wiring is intact.
Test the Powertrain Control Module	Confirm the PCM is operating correctly and not causing overvoltage.

In all three service cases, attention to the charging system’s components—especially the alternator and battery—proved crucial. Whether it was replacing the PCM, the alternator, or the battery, the solution often involved ensuring that the voltage regulation system worked within the proper parameters. For those experiencing similar issues, these steps provide a roadmap to troubleshooting and potentially resolving the problem, but professional assistance is advised for complex diagnostics and repairs.