P0A80 – Replace Hybrid Battery Pack


By Reinier (Contact Me)
Last Updated 2019-03-28
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P0A80 Replace Hybrid Battery Pack -

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What Does Code P0A80 Mean?

OBD II fault code P0A80 is a generic code that is defined as “Replace Hybrid Battery Pack”, and is set on most hybrid vehicles when the PCM (Powertrain Control Module) detects an abnormal voltage or signal in and/or from the Hybrid Battery Management System (HVBMS). On most hybrid vehicles, an abnormal voltage or signal from the HVBMS could be related to one or more of the following conditions-

  • A deviation in either the voltage or state of charge between battery modules that exceeds a predefined threshold or limit
  • A deviation in the temperature of one more modules that exceeds a predefined threshold or limit
  • An imbalance in the charge rate of one or more modules that make up the battery pack
  • An overall battery pack state of charge that does not fall within a predefined range

NOTE: While there are other possible causes of code P0A80 on hybrid vehicles, the ones listed here are the most common.

In terms of their basic principles of operation, hybrid cars are relatively simple. An internal combustion engine drives a generator that supplies both the hybrid battery pack and an electrical motor that supplies motive power to the driving wheels through a conventional differential.

At very low road speeds, typically about 10 miles per hour, the electric motor draws current from the hybrid battery pack to supply power to the driving wheels. At this point, the internal combustion drives the generator to replenish the battery pack, but does not contribute to the propulsion of the vehicle.

At speeds above about 10 miles per hour, and while the vehicle accelerates, both the electric motor and the internal combustion engine propel the vehicle, while at cruising speeds, motive power is supplied mainly by the internal combustion engine, and excess power generated is stored in the hybrid battery pack for later use.

However, to make the system as efficient as possible, the hybrid battery pack needs to be capable of storing enormous amounts of energy on the one hand, and that energy has to be controlled precisely, on the other. In terms of storage, hybrid battery packs typically consist of 28 or more cells, each of which has a typical storage capacity of 1.2 volts. On most applications, two, or sometimes more cells are connected in series, forming what is known as a battery “module”. To make up the battery pack, the modules are also connected in series, and depending on the application, the total storage capacity of a hybrid battery pack can be anywhere from 200 volts, to more than 400 volts.

Control of the stored energy is accomplished by a dedicated battery control module that monitors the temperature, state of charge, and rate of discharge of each individual cell in the battery pack. Temperature control is accomplished by multiple cooling fans that are located at strategic points around the battery enclosure. In a fully functional hybrid system, the apportioning of power between the engine and electrical motor is automatic, and requires no inputs from the driver.

Nonetheless, while second and third generation hybrid battery packs are extremely durable and reliable with expected useful lifetimes of at least ten years, they are not immune to the effects of heat, vibration, and constantly being charged and discharged. Even though most hybrid battery packs are designed to function efficiently at only about 40% or so of their capacity, it must be borne in mind that these batteries are NOT deep cycle batteries, which means that deeply discharging a hybrid battery pack can cause irreparable damage to some, if not all cells.

As a practical matter, all hybrid battery control systems incorporate measures to prevent both over and under charging. However, since all the cells in a battery pack are connected in series by a series of bus bars, corrosion of the attachment points can influence both the charge and discharge rates of individual cells, and therefore, also the temperature of individual cells. In fact, while corrosion of bus bars is arguably the most common cause of code P0A80 across all hybrid vehicles, it is also one of the most easily repaired issues, and therefore, a replacement of the hugely expensive hybrid battery pack as a result of code P0A80 is rarely required.

WARNING: It must be borne in mind that even the least powerful hybrid battery packs in use today are capable of delivering currents that are in excess of 150 Amps, which is enough to cause the fatal electrocution of an average person. Therefore, hybrid battery packs are to be considered as extremely dangerous and NOT user serviceable: all repairs, servicing, maintenance, and replacement procedures involving the hybrid battery pack must therefore only be performed by suitably qualified and experienced personnel, because making a mistake at any point during even a routine servicing procedure could kill you.  

Where is the P0A80 sensor located?

The image above shows the location (circled) of the hybrid battery pack in a Toyota Prius. The arrow indicates the location of the battery control module, which must NOT be tampered with under any circumstances, because doing so could cause severe electrical shock, and even fatal electrocution. Not shown here is the service plug, a device that effectively disables the battery when it is removed from the battery pack.

What are the common causes of code P0A80?

The most common causes of code P0A80 are similar across all hybrid vehicles, and could include one or more of the following-

  • Corrosion of connecting bus bars, resulting in the loss, or partial loss of continuity across attachment points
  • One or more defective ammeters, resulting in inaccurate charging, discharging, or state of charge information on one or more battery cells being relayed to the hybrid battery control module
  • One or more defective hybrid battery cooling fans, or clogged cooling fan air inlets resulting in uneven heat distribution across the hybrid battery pack
  • One or more defective hybrid battery cells, but note that this is rare
  • Under or over charged hybrid battery pack, but note this is exceedingly rare, and will always be accompanied by several other hybrid battery related trouble codes

What are the symptoms of code P0A80?

The symptoms of code P0A80 are much the same across all applications, and could include the following-

  • Codes other than P0A80 may also be present, and one or more warning lights may be illuminated
  • The internal combustion engine may run for longer periods than it used to, which invariably produces reduced fuel economy
  • Overall vehicle performance may suffer noticeably, particularly under hard acceleration
  • The electrical propulsion system may not be available, or in some cases, the electrical propulsion system may be deactivated by the PCM as a safety precaution until the root cause of the code is resolved

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