P0A5B – Generator Current Sensor Circuit Low


By Reinier (Contact Me)
Last Updated 2016-10-25
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P0A5B Generator Current Sensor Circuit Low Defective current sensor, Alternator, Wiring

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What Does Code P0A5B Mean?

SPECIAL NOTES: It should be noted that generic code P0A5B applies to both hybrid-car propulsion systems and conventional charging systems. In both instances, the code has the same basic meaning/definition- “Generator Current Sensor Circuit Low” which refers to the charging current generated by the system being too low, or lower than expected. Since this code also applies to highly complex hybrid systems, it is as well to bear in mind the official definition (as per SAE ((Society of Automotive Engineers)) document J2012) of the word “LOW” as used in this context: –

Low Input [shall mean] – “Circuit voltage, frequency, or other characteristic measured at the control module input terminal or pin that is below the normal operating range.”

The above definition-within-a-definition represents an important distinction between hybrid and conventional charging systems, because the term “frequency, or other characteristic” generally does not apply to conventional charging systems to the same degree that it does on hybrid systems, in which a current can be switched between AC and DC, as well as between energy levels several times before it reaches either the traction motor(s) or the battery pack.

Therefore, due to the extreme complexity of hybrid propulsion systems, this guide cannot provide detailed diagnostic and repair information for this code as it applies to hybrid systems. Diagnosing and repair fault codes on hybrid systems requires advanced professional grade diagnostic equipment, as well as above average diagnostic skills in general, and expert-level knowledge of the application in particular. For this reason, this guide will focus on diagnosing and repairing code P0A5B as it applies to conventional charging systems. As such, the information provided here should NOT be used for diagnosing any electrical issue on any hybrid propulsion system. END OF SPECIAL NOTES.

NOTE #1: With reference to this code as it applies to conventional systems, the word “Generator” is used interchangeably with the word “Alternator”, since the distinction between alternators that generate AC current and generators that generate DC current, is no longer relevant. In automotive parlance today, alternators are almost universally referred to as “generators”. 

NOTE #2: “Generator current sensor” in this definition refers to a Hall-effect sensor that monitors and largely controls the current being produced by the generator.  

OBD II code P0A5B is a generic code that is universally defined as “Generator Current Sensor Circuit Low”, and is set when the PCM (Powertrain Control Module), Body Control Module, or any other relevant controller detects a lower than expected charging voltage or current.

The charging systems of modern vehicles have developed to the point where these systems bear no relation to the charging systems of cars made a mere ten years ago. The multitude of features and electrical consumers fitted to cars today requires that the current fed to each consumer be precisely controlled to extend component life, ensure the stability of all systems, and to maintain proper communication between all control modules.

To accomplish all of the above, modern charging systems are fitted with a current sensor whose function it is to control and adapt the generator’s output to meet varying demands, while keeping the system stable overall. However, the current sensor is linked to several other controllers and modules that collectively, have the function of maintaining system stability, preserving the battery’s state of charge, as well as the battery’s state of health, while supplying sufficient current to various systems and sub-systems. Today, a typical charging system consists of a current estimation module, the aforementioned current sensor, as well as a dedicated module that performs diagnostic functions in the charging system in general, but in the current sensor in particular.

In terms of operation, the current estimation module determines the estimated amount of current required to meet the demand of all electrical consumers, which estimation is based on the current engine speed while the generator is working in a steady-state condition. This estimation is monitored by the current sensor, while the current diagnostic module calculates the condition of the current sensor based on the relationship between the estimated output current, and the actual, measured output current.

The rationale behind this convoluted way of supplying power to a vehicle’s electrical consumers is the fact that today, most vehicles are “pre-programmed” with several electrical modes, or put in another way, several power consumption “profiles”, much like PC’s have several power-saving modes to choose from to make the most efficient use of the energy it receives, while ensuring that all systems are supplied with sufficient power to keep critical systems powered-up. Below are the typical “Power Modes” found on modern vehicles, but note that not all modes will be present on all applications-

  • Charge mode
  • Fuel Economy mode
  • Voltage Reduction mode
  • Start up mode
  • Windshield de-ice mode
  • Battery sulfation mode

A full discussion of the various modes falls outside the scope of this article, but suffice to say that each mode involves different electrical consumers, which requires different levels of output current from the generator to balance the rate of current draw with charging current to preserve the battery’s state of charge at, or above 80%. All of this happens by constantly adapting the generator’s output to meet current demands, and without causing spikes or drops in the supply of current to all and/or any other consumers.

The image below illustrates the operating principles of a current sensor. As the current being measured passes through the ferrite coil the current creates a magnetic field, which is amplified by the Hall-effect sensor embedded in the coil. Based on the strength of the amplified magnetic field, other modules in the charging system calculate the actual voltage passing through the sensor, which in turn, is used by the current estimation module to calculate and/or determine the level of current output required from the generator to supply the demands of any given power mode the vehicle is in at that moment.


What are the common causes of code P0A5B?

Common causes of code P0A5B are much the same across all applications, and could include the following-

  • Defective current sensor
  • Defective alternator. In these cases, there is likely to be other charging system related codes present as well.
  • Damaged, burnt, disconnected, shorted, and /or corroded wiring and connectors
  • Open circuits. In these cases, there is likely to be other electrical system related codes present as well.
  • Poor electrical connections that could be anywhere in the electrical system, including deep inside wiring harnesses that make up the CAN bus system.

What are the symptoms of code P0A5B?

Apart from a stored trouble code, an illuminated warning light, and possibly a flat battery, the symptoms of code P0A5B are largely make and model specific. Erratic behavior by any light, system, setting, or display could be a symptom of this code, but such erratic behavior could have many unrelated causes, and it should therefore not automatically be taken as a symptom of this code. Always consult the manual for the application being worked on for detailed information on symptoms that are likely to affect that application.

How do you troubleshoot code P0A5B?

WARNING: DIY mechanics and non-dealership technicians who do not have access to professional grade diagnostic equipment, expert-level diagnostic skills, and ALL relevant technical information should NOT attempt a diagnosis and repair of this code, beyond checking for the presence of P-codes that do not have letters in them.

Moreover, since several controllers are implicated in this code, generic code readers will not be able to enter, or communicate with the CAN (Controller Area Network) bus system. As a minimum requirement, the scanner used must include all the parameters for each of the power modes present on the vehicle, which parameters must include at least the following-  


  • Generator L-Terminal
  • Generator F-Terminal
  • Battery Voltage

Body Control Module/Dashboard Integration Module/Integrated Power Module

  • Battery Current Sensor
  • Battery Voltage
  • Ignition Voltage
  • Load Shed Level
  • Idle Boost Level

NOTE: Based on the above requirements, what follows are the only diagnostic and repair steps that are available to non-professional mechanics and technicians.

Step 1

Record all fault codes present, as well as all available freeze frame data. This information could possibly be of use should an intermittent fault be diagnosed later on.

NOTE: Be aware that each power mode on all applications has specific conditions that have to be met to avoid setting a trouble code. The specific conditions that have to be met before a system will enter any given power mode vary between applications, and while there is some overlap between applications, it is important to consult the manual for the application being worked on for specific, detailed information on this issue.

However, it sometimes happens that relatively simple, or easy-to-resolve P-codes are set when a condition is not met, meaning that in at least some cases, it might be possible to resolve code P0AB5 by resolving one or more P-codes that accompanies it. Therefore, it is important to scan all systems for both pending and active P-codes as a first step in diagnosing this code.

If other P-codes are present, resolve them in the order in which they were set and stored, and always refer to the manual for detailed information on diagnosing and repairing all codes that are resolvable on a DIY basis.

Step 2

If no other codes are present, the only remaining option is to operate the vehicle with a scanner connected to be able to monitor the idle-boost and loads shedding parameters in real time. Doing this may, or may not reveal abnormal values, since the code may have been set under different environmental conditions such as high/low ambient temperatures, or perhaps high humidity conditions.

Be aware though that load shedding (dumping of current) is normal, and there is no telling if the values displayed during shedding is abnormal for that application or not. The only way to check displayed values during this test is to compare all obtained values against those obtained from an identical vehicle that is known to be trouble-free.

Step 3

If there are no pending or active P-codes present along with P0A5B, or if this code persists despite having resolved all other P-codes present, the only option remaining to non-professional mechanics is to refer the vehicle to a dealer for professional diagnosis and repair.

Codes Related to P0A5B

  • P0A59 – “Relates to Generator Current Sensor Circuit”
  • P0A5A – “Relates to Generator Current Sensor Circuit Range/Performance”
  • P0A5C – “Relates to Generator Current Sensor Circuit High”

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