2005 Toyota Prius HV Battery Case Study Code P0A80 Replace HV Battery
By Gilbert Hernandez Barsom Automotive Whittier CA 90606 www.BarsomAuto.com
Toyota Prius HV Battery •
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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. money.
Toyota Prius HV Battery •
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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 •
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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.
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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 voltage Description of how values are calculated.
Toyota Prius HV Battery •
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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. That’s 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.
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Start the vehicle being sure is in ready mode.
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Turn head lights on.
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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 •
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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 Engine compartment 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.
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 off Turn vehicle on be sure is in the ready condition. Read your data from the HV Battery.
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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.
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State of Charge is 42.50 %
Total HV Voltage very close to
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 speed Head lamps on Remove EFI fuse Allow HV Battery to discharge for 20 minutes Read data from scan tool:
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Before Cell Replaced
With State of Charge at 0%
After Cell Replaced
With State of Charge at 16.0%
Disclaimer •
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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.
