2005 Toyota Prius HV BatteryCase Study

By Gilbert HernandezBarsom AutomotiveWhittier CA 90606

www.BarsomAuto.com

Code P0A80

Replace HV Battery

Toyota Prius HV Battery

According to service manual, code P0A80 when present, will require to replace HV Battery.

The cost of the replacement goes over $3,000.00.

The HV Battery can be disassembled and repaired, saving customer money.

Toyota Prius HV Battery

In order to diagnose the HV Battery, a scan tool capable of reading HV data is required.

Our example uses AutoEnginuity scan tool. You also need High Voltage Gloves, good

understanding of basic electric circuits. A voltmeter. Do not place the HV Battery over a steel work

bench, use a wood base workbench(less conductive)

Toyota Prius HV Battery

Our sample vehicle came with a P0A80 code. We had repaired this vehicle before replacing two

cells. Customer was able to drive it for over a year, now

he came back with the same code. Codes were reset to have a clear beginning. Data from scan tool was recorded and saved for

analysis. See next screen shots.

We know this HV Battery is going bad, but our data from scan tool seems like normal.

We have 14 blocks, VBB1 to VBB14, that get monitored by the HV ECU. Each block is made of two modules (battery) of 7.2 Volts to produce a total of 201.6 Volts.

VBB1 VBB2 VBB3 VBB4 VBB5 VBB6 VBB7

Toyota Prius HV Battery

AutoEnginuity scan tool screen shot.Notice the value of Battery State of Charge and the Battery Block Voltage values.

Toyota Prius HV Battery

Our voltage values got analyzed using Microsoft Excel, trying to find a voltage variations between blocks. Voltage variation between blocks is within normal values. We found the HV total to be too high. It must be closed to the nominal 201.6 Volts.

Toyota Prius HV Battery

Highest Voltage

Column Shows voltage difference from highest voltageDescription of how values are calculated.

Toyota Prius HV Battery

The HV Battery is a combination of 28 7.2 Volt batteries connected in series. If one of them is delivering or storing less voltage than the others, the HV ECM will compensate overcharging the others. Thats why the total HV output is 34.36 volts in excess.

The next step to follow is to force the HV Battery discharge, to find the bad block.

Discharging the HV Battery

In order to discharge the HV battery, all codes must be cleared.

Start the vehicle being sure is in ready mode. Turn head lights on. Turn A/C on to the lowest temperature,

blower to the full speed.

In this way gasoline engine will run and stop as designed.

Toyota Prius HV Battery

The A/C takes the power needed to run out of the HV battery.

The 12 Volt auxiliary battery gets charged out from the HV battery.

HV battery gets charged back when gasoline engine is running.

If engine stops running unexpectedly, the HV battery will discharge itself to a lower than normal levels. Which is our goal.

2005 Toyota Prius Fuses

EFI Fuse 15A

AM2 Fuse 15A

Horn Fuse 10A

HEV Fuse 20A

Remove EFI fuse while vehicle in ready mode and leave vehicle alone for the next 30 minutes. Keep track of the State of Charge and also

The readings from batteries will show something like the next captures.

Engine compartment fuses

Snapshot after 30 minutes, Note the State of Charge. It shows Zero.

The total HV Voltage is now 246.19 Volts.The voltage variation between blocks is normal

The scan tool data did not render any results.

The total HV voltage is very high and the state of charge is very low!

This HV Battery is out of whack!

The next steps will require to remove the HV Battery out of the vehicle.

All the removing steps can be found on the service manual.

Follow all the needed precautions to avoid fatal injury.

Wearing high voltage gloves mandatory.

Place the HV Battery on the non metal workbench.

Remove the metal covers and place the HV ECM aside

Remove all the connectors that make up the HV battery, beginning on the side were the safety switch is located.

Once all the connectors are removed from one side, the HV battery becomes less harm.

Remove all the connectors on the opposite side, allowing the single 7.2 V batteries to be exposed.

1156 mini lamp

Test every 7.2 V battery under load and record the measurements. This lamp will draw about 1.2 amps.

In our case the lowest reading from all was #6 with a value of 7.3 Volts, the other cells had values of 7.80V

It seems this 0.50 volt variation will drive the HV ECM a little crazy.

1156 mini lamp

Using the same arrangement, the batteries can be load tested for specific amount of time and record a final reading for each one.

1156 mini lamp

7.50

Safe way to charge a 7.2 V battery with a 12V battery.Light bulb works like a voltage divider and also as a amp limiter to 1.3 Amps.Charge battery up to 7.5 volts.

After replacing de defective Battery with a good one. Assemble everything back into the vehicle.Install EFI fuse back. Be sure auxiliary battery is fully charged.Turn vehicle on, read codes and reset them all.Turn vehicle offTurn vehicle on be sure is in the ready condition.Read your data from the HV Battery.

Allow vehicle to run and start charging the HV Battery.Gasoline engine will turn on and off as designed.Watch voltage readings and State of Charge.

State of Charge is 42.50 %

Total HV Voltage very close to 201.60 Volts

How to verify our work

Be sure State of Charge is above 40% and gasoline engine had stop and started twice.Turn A/C to max cold and blower to high speedHead lamps onRemove EFI fuseAllow HV Battery to discharge for 20 minutesRead data from scan tool:

Before Cell Replaced After Cell Replaced

With State of Charge at 0% With State of Charge at 16.0%

Disclaimer

All our experimentation have no scientific basis.

Our repair is guarantee for one year or 12,000 miles, whichever occurs first.

If you follow our instructions and still HV Battery do not work as designed, we are sorry.

You can send us your HV Battery and we do the repair for you. Call us for more details at (562) 945 2658.

2005 Toyota Prius HV BatteryCase Study By Gilbert HernandezBarsom AutomotiveWhittier CA 90606www.BarsomAuto.com Toyota Prius HV Battery Toyota Prius HV Battery Toyota Prius HV Battery Slide Number 5Toyota Prius HV Battery Toyota Prius HV Battery Toyota Prius HV Battery Toyota Prius HV Battery Discharging the HV Battery Toyota Prius HV Battery 2005 Toyota Prius Fuses Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Disclaimer