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Hybrid electric vehicles rely on two propulsion systems: an internal combustion engine and an electric motor.

Most hybrid vehicles have a high-voltage battery pack and a combination of electric motor and generator to assist the gasoline engine. In some designs, the electric motor can propel the vehicle without starting the internal combustion engine.

As convenient as that sounds, driving a hybrid vehicle isn’t all sunshine and rainbows because it can develop issues like a conventional vehicle.

In the case of a hybrid vehicle, most issues can be traced to the battery packs, which can trigger the hybrid system malfunction warning light.

What Does an Illuminated Hybrid System Malfunction Warning Light Mean?

A hybrid system malfunction means that the vehicle is unable to operate at full capacity because of electrical issues.

A hybrid system malfunction or check hybrid system warning light is usually found in some Toyota and Lexus vehicles with a hybrid powertrain.

2022 toyota highlander hybrid toyota usa newsroom
A hybrid system malfunction or check hybrid system warning light is usually found in some Toyota and Lexus vehicles with a hybrid powertrain. Image credit: Toyota USA Newsroom.

This warning light often comes in a yellow or red color. A yellow warning light means that the vehicle is experiencing a minor issue with the hybrid system, while a red one is indicative of a more serious problem.

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What Causes the Hybrid System Warning to Pop Up?

Several electrical faults can cause the hybrid system warning to pop up, including a blown fuse, defective battery cells, inverter problems, and a worn-out or damaged 12V battery pack.

Blown Fuse

Defective fuses and exposed wiring can cause a fuse to blow. A blown fuse is indicative of a short circuit, which means that an electrical component can’t handle a strong current.

Defective Battery Cells

Each cell is a 2.1-volt battery in itself. A battery cell is made up of positive and negative plates with an insulating separator between them.

Overcharging can boil the cell’s electrolytes and overheating can warp the cell plates. A defective cell can cause the battery’s state of charge to fluctuate, affecting a hybrid vehicle’s performance.

Inverter Problems

An inverter changes direct current (DC) into alternating current (AC). Most DC-AC inverters have switching transistors that switch on at certain intervals for short pulses.

In a hybrid system, an inverter cooling system is separate from the engine cooling system. The transmission’s inverter side has its own coolant pump, switching valve, and other parts.

Once the inverter fails, the hybrid system malfunction warning light can pop up on the dash accompanied by power loss. Driving with a bad inverter can also damage the battery.

Worn-Out or Damaged 12V Battery Pack

The 12-volt battery pack on a hybrid vehicle powers the electronic control unit (ECU), computer relays, headlights, audio systems, and other accessories, reducing the power that the main battery has to churn out.

If the vehicle isn’t in ready mode, the 12-volt battery disconnects the main battery from the rest of the system. This prevents the main battery from producing a high-voltage output when it’s not needed.

You’ll notice that most of the electrical accessories won’t work once the 12-volt battery pack fails.

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What Are the Symptoms of a Hybrid System Malfunction?

A vehicle experiencing a hybrid system malfunction can exhibit the following symptoms:

  • Poor acceleration
  • Running solely on fuel
  • Poor fuel economy
  • Going into limp mode

Diagnostic Trouble Codes Associated with a Malfunctioning Hybrid System

An illuminated hybrid system malfunction warning light won’t necessarily tell you what the problem is.

Fortunately, the vehicle computer is capable of communicating by storing diagnostic trouble codes (DTCs), informing the driver of what component is causing the problem.

Here are some of the most common DTCs your vehicle could store once the hybrid system malfunction warning light pops up.

  • P08A0 – Replace Hybrid Battery Pack
  • P0A7F – Hybrid Battery Pack Deterioration
  • P0A92 – Hybrid Generator Performance
  • P0AA6 – Hybrid Battery Voltage System Isolation Fault
  • P0AC4 – Hybrid/EV Powertrain Control Module Requested MIL Illumination

Hybrid Vehicle FAQs

Below are some frequently asked questions about hybrid vehicles and system malfunctions.

2021 lexus es hybrid lexus newsroom
Most hybrid batteries can last up to 100,000 miles, according to several manufacturers. Image credit: Lexus Newsroom.

Can You Drive Your Vehicle With a Hybrid System Malfunction?

It’s best to take your vehicle to the nearest auto repair shop as soon as the hybrid system malfunction warning light pops up.

Depending on the severity of the code, there’s a possibility that you won’t be able to drive your vehicle.

Driving your vehicle while the warning light is on display can result in more damage and a more expensive repair bill if left unaddressed.

Depending on the severity of the code, there’s a possibility that you won’t be able to drive your vehicle.

Anthony Harlin, ASE Certified Master Automobile Technician

How Much Will a Hybrid Battery Replacement Cost?

You can expect to pay anywhere between $2,000 and $8,000 to replace a damaged or worn-out hybrid battery pack.

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In some cases, drivers don’t really have to worry about buying a replacement battery because they would’ve sold their vehicles before the battery reaches the end of its service life.

Can You Repair a Damaged Hybrid System at Home?

Repairing a malfunctioning hybrid system isn’t a DIY-friendly task. Hybrid systems have high-voltage components that can electrocute someone who doesn’t know how to work their way around such vehicles. In most cases, anything in high voltage is wrapped in orange, so take note of that distinction before proceeding with the repairs.

If you’re not an expert on hybrid vehicle repair, it’s best to have a trained professional do the job for you. This will ensure that all steps and protocols for diagnosis and repair are followed correctly.

How Long Do Hybrid Batteries Last?

Most hybrid batteries can last up to 100,000 miles, according to several manufacturers.

Why Are Hybrid Batteries So Expensive?

Hybrid batteries are more expensive than traditional automotive batteries mainly because they have a longer lifespan than their counterpart.

Key Takeaways

An illuminated hybrid system malfunction warning light usually points to electrical faults in components like the inverter, battery cells, 12V battery pack, or fuse.

Once the computer detects a fault in the system, you can expect to see a drop in acceleration output and fuel economy.

Make sure to have a professional mechanic take a look at your vehicle before going out for a drive. It’s also not advisable to work on hybrid vehicles on your own if you’re not trained in repairing such systems.

About The Authors
Anthony Harlin, ASE Certified Master Automobile Technician
Reviewed By Anthony Harlin, ASE Certified Master Automobile Technician

Technical Reviewer at

Tony Harlin is a Master Gas and Diesel Diagnostic Technician with over 18 years of experience. He works full-time at a large independent automotive shop as a driveability and repair technician working on all types of vehicles with a focus on diesels. ASE certifications include A1-A9, L1 and L2, as well as X1.

CarParts Research Team
Written By Research Team

Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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