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Battery Sensor

Many modern cars have a battery current sensor. It might also be called a battery management or monitor sensor, or simply battery sensor. Typically, a battery sensor is installed on the negative battery terminal or on the cable. It might be installed on the positive terminal. Some cars have two sensors, one on each terminal.
 

A BMW battery sensor
A BMW battery sensor

How the battery sensor works: it measures the current to and from the battery. It may also monitor the voltage, state of charge and state of health of the battery (aging). In some cars, it even measures the temperature of the battery.

The vehicle computer (Body control module BCM or Powertrain control module PCM) uses these inputs to precisely adjust the charging system voltage, idle speed and other parameters for better fuel efficiency and longer battery life. This system is called Power or Battery Management System or BMS. If the system detects that the battery is getting weak, it may turn off some electrical accessories (load shedding), such as the navigation, heated steering, heated seats, etc., to save the battery power. In this case, the computer will display a warning message on the instrument panel.



The function of the battery sensor is particularly important in vehicles with Stop-Start feature, as the battery management system must verify that the battery has enough charge to re-start the vehicle. If the battery is low on charge, the Stop-Start feature is disabled. The charging system current is also often higher in vehicles with Stop-Start feature. For this reason, in some vehicles, if the sensor has been disconnected or the battery has been replaced, the Stop-Start feature might not work for some time, until the computer (BCM or PCM) re-learns the parameters of the battery.

Many electrical problems, including issues with the battery current sensor can be caused by loose or corroded battery terminals or moisture/corrosion around the battery sensor. To function properly, the battery sensor must be clean and dry, and the pole terminal (battery head) must be tight.
 
Battery sensor problems
The most common problem is when the dirt, moisture or battery acid get into the sensor and damage or short it. 
It may cause variety of electrical problems including a no-start. A battery sensor is a fragile device and can also be damaged when servicing or removing the battery.

If a car has a battery current sensor and additional electrical accessories are connected directly to the battery negative terminal, it may cause problems, because the current will bypass the battery current sensor and its readings won't be accurate.

In many vehicles, a bad battery sensor can cause the Stop/Start system not to work. BMW calls their version "Intelligent Battery Sensor or IBS"

Location of a BMW IBS sensor


Replacement
Replacing the battery sensor will be expensive. In some cars, a battery sensor comes together with the battery cable. It's best to not break it. 

If there is a fault related to the battery sensor, the first step is to check it visually for corrosion, cracks, physical damage, loose battery terminals or battery cable connections, corroded pins at the connector or broken wires. If there are any added electrical accessories that are connected directly to the negative terminal bypassing the battery sensor, this may also cause problems.



Replacing/charging a battery in a vehicle with a battery sensor
There are some precautions when replacing the battery if a vehicle has a battery current sensor. For instance, some manufacturers advise to disconnect the battery sensor first, before disconnecting the negative battery terminal. It's also important to use the replacement battery of the correct type.

For example, some vehicles with the Stop/Start system have a special Absorbed Glass Mat (AGM) 12-volt battery, which is sensitive to overcharging. When replacing, an owner's manual may recommend using only the AGM battery.

In some vehicles, a new battery might need to be "registered" with the battery management system using a scan tool (e.g. BMW). If the battery replacement is not registered, the battery (power) management system might not function properly. In some Ford vehicles, the battery management system might need to be reset after the battery has been replaced.

It is also important where to connect the wire clamps when boosting or charging the battery with a battery sensor.  At least, check your vehicle owner's manual or do some research before replacing the battery. 

Considering all this, it might be a good idea to change the battery at a dealership. If you can afford such a complex car, I'm sure you can afford the dealership charges as well, "to prevent stories that touch" or "oga abeg".

Twitter and Instagram; @VverteAutoSevcs
Email; vverteautosevcs@gmail.com
Phone; 09137103730



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