Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that the car's computer is detecting that the electrical system's voltage is too high, like when a battery is overcharged.
The vehicle's powertrain control module (PCM) monitors the electrical system's voltage. If it detects a voltage level higher than the expected range, it triggers this code.
P1891 is set when the PCM detects that the system voltage is above the threshold level, which could indicate an issue with the alternator, voltage regulator, or battery. High voltage can damage electrical components and affect vehicle performance.
• Battery warning light on
• Dimming or flickering lights
• Electrical components malfunctioning
• Faulty alternator
• Defective voltage regulator
• Wiring issues or short circuits
PCM: Powertrain Control Module, the vehicle's main computer.
Voltage Regulator: A device that maintains a constant voltage level.
• Check battery voltage with a multimeter.
• Inspect alternator output for overcharging.
• Examine wiring and connections for damage or shorts.
• Replace faulty alternator.
• Repair or replace voltage regulator.
• Fix any damaged wiring or connections.
• Multimeter
• Wrench set
• Screwdriver set
$150 - $500
Moderate
• Ford F-150
• Chevrolet Silverado
• Toyota Camry
• Regularly check battery and alternator health.
• Ensure all electrical connections are secure.
• Avoid overloading the electrical system.
Electrical System Issue
• Do not ignore the battery warning light.
• Have your vehicle's electrical system checked regularly.
Check with your vehicle manufacturer for specific warranty coverage on electrical components.
This code has been commonly associated with alternator and voltage regulator failures in vehicles with higher mileage.
High – Excessive voltage can quickly damage electrical components.
Driving with electrical issues can lead to vehicle breakdowns and safety hazards.
• Engine running
• All electrical accessories off
The alternator and voltage regulator are typically located at the front of the engine, driven by the serpentine belt.
Q: Can I drive with a P1891 code?
A: It's not recommended to drive with this code, as high voltage can damage electrical components.
Q: How do I know if my alternator is overcharging?
A: Use a multimeter to check the voltage at the battery terminals. It should be between 13.5 and 14.5 volts when the engine is running.
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