Common Prius HV Battery Problems and Their Uncommon Counterparts.
So, you're driving your Prius then suddenly, your dashboard lights up like a Christmas tree, there's a big red triangle, and your lcd is showing you that the car has a problem. When this happens there are many different things it can be, inverter, corroded HV lines, or even a low 12 volt battery. To properly diagnose whether or not the HV battery is to blame for these codes, you must look at what DTC's your Prius is showing, and how it is acting.
Most every time we've seen a Prius come into our shop for a battery repair it's either had P0A80 or P3000. For most scanners the P0A80 code simply reads "replace hybrid battery" or "hybrid battery pack failure". Both of these codes simply mean that there was an HV Battery malfunction. Many times, these codes will come alongside other P30xx codes. These extra codes can help diagnose what exactly is wrong with the battery and can help you make an informed decision on how to go about your repair. Often times with any of these codes we recommend a full rebuild of the harness and battery to ensure that your repair lasts.
P3030, or "HV line snapped" is a code given when there is a very large discrepancy in either the voltage levels of the battery, or the voltage level of the entire battery. When we say "very large discrepancy" we mean that there is a line reading absolutely 0 volts. For example, in a second generation Prius, there are 14 cell blocks and a total of 28 cells. These individual cell voltages are read by the ecu in pairs, therefore 2-7.2 volt cells should read at least 14.4 or more. With a P3030 code there is a high chance that one of these block voltages will read "0". This is usually caused by a broken and corroded voltage sensor wire, however there have been times where an entire battery cell will read 0, causing this code to appear.
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| The corrosion on picture 1 will eventually lead to a full breakage of picture 2 |
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| A full voltage line "snapped" is caused when there is full loss of voltage read. |
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| A cell rupture, though uncommon, could cause the same p3030 code, among others. |
The main reason for most hybrids batteries going bad is that there's a cell that loses charge before the others and drops voltage. Many different things cause this such as electrolyte leakage, cell element deterioration, stratification or crystallization of cell element, impact and overheating. Hybrid batteries are run in a series circuit, meaning that all the batteries are run end to end, adding up the voltages to make one large high voltage battery. Eventually after many charge/discharge cycles, the battery will lose it's balance. The balance is how close the cell voltages and SOC (state of charge) are to each other. When a cell loses it's SOC it's voltage drops and causes problems within the circuit. We've seen this lead to the failure of multiple cell blocks as well as the rupture of one or more cells. This rupture issue is uncommon, however you can prevent it by getting it repaired asap. Prolonged use of a compromised battery can cause more and more problems as you drive.
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| A rare failure seen on a 2001 Prius. All 38 cells expanded or ruptured. Prolonged drive on a compromised battery could be to blame. |
P3006, or "Battery Levels are unusually different". This code is given with the state of charge on individual blocks read "outside of the range" of the others. For example if cell block 14 and 5 are reading 14.4 volts while the rest of the blocks are reading 17.0 volts the car will trigger this code. What this means is that either one or both cells in either block has a low state of charge caused by deterioration. Often times this also means that the voltage sensor wires are corroded, but just enough to cause enough resistance for the computer to read that block as being low. In either case we recommend that the battery is rebuilt simply because if there's corrosion on the terminals and sensor wires, there is crystallization inside of the battery cell itself causing the voltages to read lower, and lower. This code usually comes in tandem with the P0A80 code or the P3000 code.
P3011-P3029 codes indicate individual block malfunctions. These codes appear in the 1st, 2nd, and 3rd generation prius' according to their block count. 1st gen has 19 blocks, and 2nd and 3rd gens have 14 blocks. P3011 starts at block 1 and P3029 ends with block 19. This code is triggered in a similar manner to how the P3006 code is triggered, just on a more specific level. This basically just means that that particular cell block is below the systems voltage range. When any of these codes are triggered it means the cells need to be replaced. We recommend that with any of these codes you get a full battery rebuild. As the cells deteriorate over time, one or more will start to fail. If you simply replace a failed one, another older one is likely to go bad soon after.
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| A swollen cell can throw different voltage readings than it's neighboring blocks, causing individual block codes. |
Ecu Malfunctions
In each hybrid battery in a Prius there is a battery ECU. This ECU records the temperatures and voltages, computes them, then sends those readings to the cars main computer. The computer takes these readings and decides whether or not there is a problem with the battery. As a vehicle component, the ECU is prone to failure, as with every other vehicle part. Fortunately ECU malfunction is not as common as a battery cell malfunction or a battery harness malfunction. Often times the car can be saying that there is a problem with the computer, when the problem is within the harness itself. ECU malfunctions can only be diagnosed by a professional battery re-builder, dealer, or a shop with a dealer computer.
There are codes that can appear on an ordinary code scanner, however often times it can be very indecisive whether the ECU is actually bad.
P3001 or "Battery ECU Malfunction" indicates that the ECU is bad and needs to be replaced. This code may be triggered by either yes the ECU being bad or no by something being unplugged, shorted, or corroded.
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| Burnt harness plug exterior causing symptoms of a bad ecu. |
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| Burnt pins on an ECU port causing symptoms of a bad ECU. Repair is possible on the pins however, if the damage is on the ECU board itself it will need to be replaced. |
Summary
All of these codes are the most common codes you see with HV battery malfunctions in a Prius. Most of these codes can be read using a handheld code scanner or by being scanned by a shop or even some parts stores. Now, proper diagnostics can only be achieved by a trained professional as the hybrid system in a Prius has many variables and components. If it is deemed that yes you need to replace or get your battery rebuilt, we recommend that you decide on how much money you're willing to spend, then consider your options accordingly. Buying a brand new battery from Toyota would come with a long warranty but would cost between $3000-$4500. We've even heard from one customer that the dealer wanted to charge $5000, Ouch! There are also many different battery re-builders, including us. We recommend that you take care and caution when looking around for a good re-builder. How is their price? Do they have a good warranty? Do they have a lot of complaints? Are they very hesitant to give you straight answers? Are they a real business with a permanent location? Do they just put a volt meter to the battery can call it good, or do they use real testing equipment such as load analyzers and chargers? These are all things that you need to consider when going with a re-builder. One thing you need you always remember, if you own a hybrid vehicle, you will eventually need a battery. Just as cars brake down, the failure rate for all batteries is always eventually 100%. Look, think, and know. With the right course of action you will be sure to have a great experience with owning a hybrid vehicle.
