Why can a faulty IBS sensor deactivate the start-stop function even though the battery is still supplying sufficient voltage?

The battery voltage alone is not sufficient to activate the start-stop function. The energy management system also assesses the state of charge (SOC), state of health (SOH) and available starting power (SOF). If the IBS returns implausible readings or communication is lost, the system uses default values and, as a precaution, deactivates the start-stop function to preserve the starting capability of the engine.

Why can the symptoms of a faulty earth connection and a faulty battery sensor be the same?

The IBS measures all charging and discharging currents via the earth path at the negative terminal of the battery. Corroded or loose ground connections lead to inaccurate current measurements and calculations of SOC, SOH and SOF. Consequently, this can lead to diagnostic errors, reduced comfort or incorrect alternator control, even though the sensor itself is technically in perfect working order.

Why is battery registration frequently required after installation?

When a battery is registered, the energy management system receives the information that a new battery has been installed alongside the type and capacity. Any stored ageing parameters are also reset during the process. Otherwise, the control unit will continue to use the data from the old battery, which may lead to inappropriate charging strategies, inaccurate calculations of the battery condition and reduce the lifetime of the new battery.

How important is battery temperature when calculating the state of charge?

Battery temperature has a significant effect on capacity, internal resistance and chargeability. The temperature value is therefore continuously factored into the calculation of SOC, SOH and SOF. The available starting power drops significantly at low temperatures so the energy management system adjusts the alternator control and consumer control accordingly.

Why should LIN communication always be checked in the event of an IBS fault?

The IBS transmits measured values to the energy management system via the LIN bus or manufacturer-specific interfaces. Communication faults can also lead to missing sensor data and the use of substitute values. Fault memory entries frequently occur, comfort functions are deactivated or the scope of the alternator control functions is restricted as a result, even though the sensor itself is not malfunctioning.

Why is it often not enough to clear a fault memory entry after an IBS repair?

Following work on the battery system, many vehicles require additional initialisation procedures. Depending on the vehicle design, it may be necessary to register the battery, reset the energy management system or calibrate the IBS. This is the only way to provide the control unit with access to the correct reference values for calculating the battery condition and controlling the alternator.

Why does an increase in quiescent current lead to reduced comfort, even when the battery is in working order?

A persistently high quiescent current reduces the battery’s available energy capacity. If the energy management system detects this condition via the IBS, individual comfort consumers or control units are switched off, depending on the operating strategy. These measures are purely designed to ensure the vehicle is capable of starting and it should therefore not be unconditionally assumed that the deactivated electrical consumers are faulty.

Which real-time data is particularly useful when diagnosing the IBS?

To ensure an accurate diagnosis, in addition to the fault memory, particular attention should be paid to the battery voltage, charging and discharging current, battery temperature and the calculated condition parameters SOC, SOH and SOF. In addition, checking the LIN communication and the alternator control system provides important clues as to whether the fault is caused by the sensors, the power supply or data transmission.

Intelligent Battery Sensor (IBS) – Design, Function and Diagnostics

HELLA TECH WORLD – The Workshop’s Friend

IBS as the central measurement and control unit:
The Intelligent Battery Sensor (IBS) continuously monitors the current, voltage and temperature of the starter battery and provides the measurement data that forms the basis for the overall energy management system in modern vehicles.
Precise calculation of the battery state:
The IBS uses the measured values to calculate the state of charge (SOC), state of health (SOH) and state of function (SOF) parameters which control the alternator control, start-stop system and load management, among others.
System integration via vehicle communication:
The microprocessor integrated in the sensor processes the measurement data and transmits it to the battery management system, normally via the LIN bus. The charging strategy and other power supply functions are then derived from this data.
Systematic diagnosis prevents mix-ups:
Typical faults are often caused by corrosion, loose earth connections, faulty batteries, wiring or LIN bus faults, and incorrect battery registration, and can be narrowed down by carrying out a visual inspection, analysing diagnostic data or battery test.
The battery must be registered after replacement:
After replacing the starter battery, on many vehicles the battery data must be registered in the energy management system and initialised or calibrated if necessary to ensure the correct charging strategy is applied.

The following technical information and practical tips have been compiled by HELLA to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for suitably qualified personnel only.

The smart battery sensor in modern energy management

Energy management in modern vehicles has advanced considerably in recent years. The vehicle battery used to be purely a store containing the energy required to start the vehicle, whereas now it plays a central role in the complex on-board electrical system. Vehicles contain many electrical consumers, start-stop systems, comfort features and driver assistance systems that draw large quantities of power. They must also meet statutory requirements to reduce fuel consumption and CO₂ emissions.

To make sure these requirements are met, simply measuring the battery voltage is no longer sufficient. An Intelligent Battery Sensor (IBS) is therefore used in modern vehicles. This continuously monitors the condition of the starter battery and provides the energy management system with all relevant measurement data.

Today, the IBS supports numerous functions such as start-stop operation, intelligent alternator control, battery diagnostics, load management and battery registration. Even small measurement deviations can restrict comfort functions or lead to error codes being logged in the energy management system.

Tasks of the IBS sensor

Most manufacturers fit the IBS sensor directly to the negative terminal of the starter battery. It does more than simply monitor the battery’s condition. It logs the relevant electrical parameters and therefore is the central measuring unit on which the entire energy management system is based.

The main tasks:

Continuous measurement of the battery voltage
Measurement of the charging and discharging current
Measurement of the battery temperature
Calculation of the State of Charge (SOC)
Calculation of the battery condition, or State of Health (SOH)
Determination of available starting power, or State of Function (SOF)
Monitoring the quiescent current
Communication with the energy management control unit
Provides the basis for intelligent alternator control

The measured values are continuously transmitted to the battery management system. The amount of electrical power currently available is therefore always known.

1. Mounting bolt for earth cable 2. Pole terminal 3. Sensor module in housing 4. Data bus plug connection 5. Shunt at sensor

Circuit board with microprocessor and temperature sensor

Design and function of the Intelligent Battery Sensor

The battery sensor is a mechatronic component that monitors the battery condition.

In the context of a battery sensor, ‘intelligent’ means the sensor has an integrated microprocessor with software component. It can be split into mechanical, electronic module and software parts.

Mechanical part

The mechanical part is the battery terminal with earth cable which connects to the battery.

It performs the following tasks:

Establishes the electrical connection between the body and the negative terminal of the battery
Holds the sensor element for current measurement
Holds the electronics module
Establishes thermal contact between the negative terminal of the battery and the temperature sensor
Earth connection for the IBS (power is supplied via a separate cable)
Protection of electronic components

Electronics module

The electronics module detects voltage and measures current flow and battery temperature.

It consists of the following components:

Circuit board containing the evaluation electronics
Measuring resistor for current measurement (shunt)
Temperature sensor

The current is measured using a high-precision shunt resistor. All charging and discharging currents flow through this measuring resistor. The electronics calculate the current battery current based on the resulting voltage drop. Depending on the vehicle, measuring ranges over ±1000 A can be recorded. Whilst measuring the current, the sensor continuously monitors the battery voltage. Even slight changes in voltage provide important information about the state of charge and insights into the battery condition. A built-in temperature sensor continuously measures the battery temperature. As temperature influences battery capacity, it is factored into all energy management calculations. At low temperatures for example, the available starting power drops significantly. The electronics module processes all measured values and complex calculations.

These include:

Power integration
Plausibility checks
Ageing models
Temperature compensation
Self-diagnosis

The data is then transmitted digitally to the vehicle electrical system control unit.

Software

As the Intelligent Battery Sensor is essentially a fully-fledged control unit, it has its own programme. Just how this is implemented varies from manufacturer to manufacturer, but the basic principle is similar across most systems. The battery model is the core of the software.

This is where the measured variables are linked to stored characteristic maps and mathematical models.

The following are taken into account, for example:

Battery type (AGM, EFB, wet cell)
Temperature
Ageing
Charging and discharging history

The battery model replicates the battery’s actual behaviour as accurately as possible.

Schematic diagram of an IBS sensor. The ASIC is the central electronics of the Intelligent Battery Sensor. It measures the physical variables current, voltage and temperature, and processes the measurement data acquired.

Communication and system integration

The measured values from the IBS sensor are transmitted via a communication line to the higher-level control unit, such as the engine control unit.

The measured values are queried whilst the vehicle is in motion and when it is stationary.

Depending on the manufacturer, communication takes place via:

LIN bus (most common)
BSD interface (e.g. BMW)
CAN bus (less commonly, directly)

In current vehicle generations, the IBS sensor communicates almost exclusively via the LIN (Local Interconnect Network) bus. The LIN bus provides a cost-effective serial communication connection between sensors and control units. The battery management control unit acts as the LIN master, whilst the IBS acts as the slave.

The information transmitted via the LIN bus includes:

Battery voltage
Battery power
Battery temperature
Battery, state of charge
Error messages
Diagnostic information

If LIN communication fails, the energy management system often uses alternative values. This can restrict various convenience features.

Calculating the battery condition

The IBS not only measures electrical quantities, it uses them to calculate various parameters that allow conclusions to be drawn about the battery condition.

State of charge (SOC)

SOC describes the current state of charge of the battery.
It is calculated based on current consumption, charging cycles, battery voltage and temperature.
The value is stated as a percentage.

State of health (SOH)

SOH describes the state of health of the battery.
The useful capacity of the battery decreases as its age increases.
The energy management system takes this value into account when controlling the alternator and during start-stop operations.

State of function (SOF)

The SOF describes the currently available starting power.

This takes a range of factors into account, including:

Temperature
Internal resistance
State of charge
Ageing

If the SOF falls below a defined threshold, the start-stop function, for example, is deactivated.

Intelligent alternator control

The IBS is the foundation of modern alternator control systems. In older vehicle generations, the alternator was operated continuously at a more or less constant voltage, whereas in modern systems the alternator voltage is controlled based on the load condition, battery state and operating strategy. The energy management system uses the data supplied by the IBS to determine when to charge and at what power level.

Typical strategies include:

charging more when coasting
reducing alternator output during acceleration
increasing alternator output prior to start-stop cycles
recharging based on requirements

This helps reduce fuel consumption and CO₂ emissions.

Quiescent current monitoring

Once the vehicle has been parked and locked, the vehicle electrical system initially remains active. Control units store operating data, comfort systems shut down their functions, and communication networks gradually switch to idle mode. The vehicle bus only becomes fully inactive once the run-on phase of all relevant control units is complete.

Until then the battery sensor continuously monitors the current drawn from the battery. The energy management system can therefore detect whether electrical energy consumption falls to the correct level once the system has been switched off, or whether a consumer or a control unit remains active.

If the energy management system detects an excessively high quiescent current, various measures can be taken.

This could be:

Switching off individual comfort-related consumers
Limiting interior lighting
Switching off control units
Deactivating the parking heater
Saving a diagnostic entry

If a consumer has been switched off this does not necessarily mean it is faulty. This is often a response to the battery being low on charge.

The aim is to ensure that enough energy is still available to start the engine.

Interaction of AGM and EFB batteries with the IBS

Modern start-stop systems predominantly use AGM (Absorbent Glass Mat) or EFB (Enhanced Flooded Battery) batteries.

There is a significant difference in the charging behaviour, internal resistance and cycle life of these battery types compared to conventional wet cells.

The IBS takes these characteristics into account when calculating the state of charge.

If an incorrect battery is installed or the battery is not registered, the state of charge calculated by the energy management system may be inaccurate.

Possible consequences are:

limited start-stop function
reduced battery life
incomplete battery charge
Incorrect entries in energy management records

Technical data

Operating voltage range	Single-voltage (6 – 16.5 V)
Rated voltage	12 V
Polarity reversal voltage	– 16.5 V/60 s
Test voltage	13.8 – 14.2 V
Operating current	10 mA
Quiescent current	≤ 200 μA
Nominal resistance (shunt)	68 μΩ
Permanent load current	± 175 A
Maximum current	1,500 A
Temperature range	-40 °C to +105 °C
Re-heating temperature	+105 °C to +120 °C
Storage temperature	-20 °C to +55 °C
Protocol	LIN 2.0 or higher
Protection class	IP 6K9K
Permissible pole terminal tightening torque	5 Nm ± 1 Nm
Max. battery capacity	500 Ah
Approved	ECE R10

* Extract from the technical specifications

Technical data may vary depending on the design.

Pin 1: Battery voltage B+ and pin 2: LIN bus — Pin 1: Battery voltage B+; Pin 2: LIN bus

Maintenance and repair instructions

Battery registration using the diagnostic tool

Battery replacement and battery registration

The battery in many makes of vehicle must be registered after replacing the starter battery.

Data is stored in the energy management system, including:

Battery capacity
Battery type
Manufacturer code
Serial number

When the battery is registered, all ageing parameters are reset. If this is not done, the energy management system will continue to use the data from the old battery. Consequently, an incorrect charging strategy may be adopted and the new battery lifetime curtailed. Depending on the vehicle manufacturer, the battery is registered using a suitable diagnostic tool.

Common causes of errors

Faults in the IBS sensor are often not caused by the sensor itself.

Some of the most common causes:

Corrosion of the battery pole
Loose pole terminals
Damaged earth leads
Undervoltage
Faulty battery
Moisture in the sensor
Cable breaks
LIN bus faults
Incorrect battery registration
Mechanical damage

Systematic diagnosis avoids parts having to be replaced unnecessarily.

Typical OBD fault profiles

Faults relating to the IBS or energy management system often lead to entries in the error log. Error codes and designations vary depending on the vehicle manufacturer. OBD fault profiles can typically be traced back to communication faults, implausible sensor signals or incorrect battery status detection.

Common fault profiles include:

Communication error between the IBS and the control unit (LIN bus)
Battery sensor – implausible signal
Battery sensor – short circuit or open circuit
Battery condition cannot be calculated
Quiescent current too high
Battery charge insufficient
Start-stop system deactivated due to battery condition

Day-to-day workshop experience shows that these faults are often accompanied by comfort restrictions. Examples of this are deactivated start-stop function, reduced alternator output, or messages such as ‘Charge battery’ or ‘Energy-saving mode active’.

A diagnostic device can be used to read out the latest measurements such as the voltage, current or temperature of the battery.

Diagnostics

The diagnosis of the battery sensor should always begin with a visual inspection. In particular, the following should be checked for damage or corrosion:

Battery poles
Ground connections
IBS plug connections
Cable routing

The control unit is then diagnosed using a suitable diagnostic tool. Depending on the vehicle, system or diagnostic tool, the following information may be taken into consideration when troubleshooting:

Fault memory
Live data from the IBS
LIN communication
Battery voltage
Charging and discharging current
Battery temperature
State of charge
Alternator regulation

The troubleshooting itself and successful repair work is based on the control unit communication data.  It is also advisable to check the battery using a suitable battery tester.

When replacing the IBS sensor, the manufacturer’s specifications must be followed.

The sensor must not be mechanically modified or opened.

Following work on the battery or IBS, the following measures may be required, depending on the vehicle manufacturer:

Battery registration
Resetting of the energy management system
Calibration of the battery sensor
Clearing the fault memory
Functional test of the alternator control system

Failure to initialise the system may lead to errors when calculating the battery condition.

IBS sensor – check and replace

We’ll take you through the process of testing and replacing the IBS sensor, explaining what you need to bear in mind, using examples. The most important work steps at a glance.

Conclusion

The IBS sensor has evolved from a simple measuring sensor into a key component of energy management. By continuously monitoring current, voltage and temperature, and calculating operational parameters such as state of charge, state of health and state of function, the IBS ensures that the prerequisites for the supply of energy in modern vehicles based on requirements are met.

The increasing prevalence of start-stop systems, AGM and EFB batteries, software-controlled energy management strategies and 48-volt electrical systems means that it is becoming increasingly important to diagnose the IBS correctly. A systematic check of the sensor systems, LIN communication and battery registration increases the troubleshooting accuracy and helps avoid unnecessary component replacements. Professional diagnosis and repair of energy management systems are therefore essential nowadays in workshop operations.

The information in this technical article is intended solely to provide general technical information on the design, operation and diagnosis of Intelligent Battery Sensors (IBS) and modern energy management systems. The systems, diagnostic procedures and repair measures described may vary depending on the vehicle manufacturer, model, year of manufacture and generation of the control unit.

When carrying out diagnostic, testing and repair work, always follow the vehicle-specific manufacturer’s instructions, repair manuals and the currently applicable service and safety regulations. In particular, work on 48-volt vehicle electrical systems must only be carried out in accordance with the manufacturer’s specifications and in compliance with the necessary safety measures.

The OBD fault profiles and diagnostic messages shown here are typical examples from workshop practice and may vary depending on the vehicle manufacturer and diagnostic system. A definitive fault diagnosis can only be made on the basis of manufacturer-specific diagnostic data and a systematic inspection of the entire system.

Subject to technical modifications and further developments to vehicle and diagnostic technology.