Toyota Hybrid Battery Tests You Can Do and Those You Should Not Attempt If You Want to Save Yourself a Trip to the Morgue

If you are a DIY mechanic, you are no doubt tempted to dig into your spouse's hybrid and learn a little more about how to assess its battery and make sure it is running as well as its gasoline-driven engine.

However, a good reminder to DIY mechanic types was recently posted on the Toyota Maintenance YouTube channel:

This video may be called ‘How to test a Toyota hybrid battery’ but it's by no means a how-to video. I am always encouraged to help you work on your vehicles. If you are interested in this case, however, absolutely not. I will say it clearly at least once: Don't do these things. Don't play with it These hybrid batteries are extremely dangerous It can kill you if you do not know the safety precautions and do not have proper training from Toyota."

To make his point just a little clearer, note the two-man EV battery disassembly image showing one of the techs holding an insulated hook as a safety measure.

About the Video

The hybrid vehicle "show and tell" is a 2006 Highlander from an earlier video that was diagnosed with a failing hybrid battery problem due to some cell modules that had gone bad in one of the three hybrid battery packs.

The source of the problem was a common water intrusion problem with Highlander sunroofs that are not maintained well by their owners.

Although this is not an instructional how-to video, it is very useful in that it provides an in-depth look at a battery pack and how it is serviced by a trained EV mechanic. This video will add to your automotive knowledge bank in case you are ever told you need a new hybrid battery.

Follow along with the host as he discusses:

1. What an EV battery pack looks like in a Toyota.
2. Where to expect eventual corrosion problems in the busbar.
3. How to tell which cell ends are positive and negative.
4. How to test each cell in a pack with a simple voltmeter and what voltage a good cell will read.
5. An example of what a bad cell will show on a voltmeter test.
6. Why a salvage yard might be your best friend.
7. Why a Toyota goes dead even with just a bad cell or two.

How To Test Toyota Hybrid Battery

What You Can Do With Your Hybrid Battery Without Training

If the "Check Hybrid System" light or triangle warning is on, that's a strong sign the battery (or related component) has a problem.

Although non-EV trained DIY mechanics are encouraged NOT to dig around in an unfamiliar EV system, there are two things the DIY mechanic can do safely:

1. Use the Built-in Diagnostic Mode (Hidden Menu)―Your Highlander's multi-information display has a hidden diagnostic mode. To access it:

• Turn the ignition to "ON" (do not start the car).
• Press and hold the "Info" button.
• While holding "Info," turn the headlights off and on 3 times.
• The system will enter a diagnostic mode.
• This can show battery voltage and other system data, but it's not as comprehensive as a real scan tool.

2. Use an OBD2 Scanner with Hybrid Support―A standard OBD2 scanner won't tell you much about the hybrid system. You will need a scanner that supports Toyota hybrid-specific data. However, if you can afford one, it will show you:

• Individual battery block voltages
• Internal resistance
• Temperature data
• State of charge (SOC)
• Trouble codes related to your hybrid battery

How to Get Hybrid Battery Training

If you are motivated, you can learn how to work on a hybrid battery up to the level of diagnosing and removing individual bad cells and putting it all back together safely.

First Step: Watch this instructional video on how Toyota hybrid batteries work.

Second Step: If the first step encourages you to upgrade your DIY skills regarding EV hybrid batteries and the EV electrical system, there is an interesting opportunity to get schooled on EVs and their repair at Weber State University.

For a taste of why this is a recommended education resource, watch a few YouTube videos of Professor John Kelly as he teaches wide range of informative, in-depth videos through Weber State University.

Weber State University offers three programs consisting of two online and one Hybrid and Electric Vehicle Bootcamp for 7 days at a tuition cost of $375, $735, and $2,000 respectively.

Two Good Reasons Why You May Not Want to Become a Trained EV DIY Mechanic to Save Money on Your Hybrid

Learning more about how to repair your EV is commendable, and perhaps you can envision saving money by replacing the faulty cells yourself rather than spend around $6,000 for a new hybrid battery replacement.

However, there are at least two problems with this:

1. Toyota does not sell individual hybrid battery cells.
2. Even if you find replacement cells, there is the problem of battery balancing―mixing older battery cells with new battery cells can be problematic and lead to more hybrid battery troubles and repairs. Variations in charge levels between cells can lead to issues like reduced battery lifespan, decreased efficiency, and even safety concerns that will require factory-level repair skills and equipment.

In other words you are better off financially, learning how to maintain your EV battery to last its longest and being prepared to possibly have to replace it down the road than taking the time and money to DIY an EV Hybrid battery.

But where's the fun in that!

If you have ever attempted to repair your EV battery, tell us about it in the comments section below. Would you recommend learning about how to work on your car's EV battery?

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Timothy Boyer is an automotive reporter based in Cincinnati who currently researches and works on restoring older vehicles with engine modifications for improved performance. He also reports on modern cars (including EVs) with a focus on DIY mechanics, buying and using tools, and other related topical automotive repair news. Follow Tim on Twitter at @TimBoyerWrites as well as on Facebook and his automotive blog "Zen and the Art of DIY Car Repair" for useful daily news and topics related to new and used cars and trucks.