When a vehicle comes into our shop for repair, we make several routine checks before we get into our diagnostic routine. Checking the battery and charging system on the car we are working on falls into this category. With more and more electrically dependent components added to the typical vehicle comes more demand for the battery and charging system to be at peak performance, especially when diagnosing transmission and driveability issues.
At the focal point of a vehicle’s electrical system is the battery. We all know by now that a weak battery must be addressed before getting into a deeper level of diagnostics. Sometimes, jumping start, charging, or replacing a battery may be necessary to get the system to proper operating condition. Fixing a battery-related concern seems simple enough given our experience as technicians; however, on late-model vehicles, they added some need-to-know items to consider before you place a wrench on a battery terminal to fix a problem. Otherwise, you could end up creating unnecessary headaches and added expenses. Let’s take a closer look at what is different on the battery side of GM vehicles.
THE ABSORBED GLASS MAT (AGM) BATTERY
A new generation of batteries has become more prevalent in late-model vehicles. While GM doesn’t have this market cornered, starting about 2015, most of their cars come equipped with an AGM. 
With a similar construction to the conventional lead acid battery, absorbed glass mat batteries have distinctive properties that make them more desirable than their predecessors. Here are some of the notable advantages of AGM batteries:
- Maintenance-free and spill-proof design: the acid solution is absorbed into a fiberglass mesh.
- Deep duty cycle: the suspended fluid allows up to 50 percent discharge while maintaining full amperage capacity.
- Longer lasting; the release of hydrogen and oxygen gases during normal charging is regulated by a venting system, which allows for less water loss.
A typical AGM battery is good for up to 60,000 starting cycles, compared to a flooded lead acid battery at 20,000. With Stop/Start technology becoming more common, most manufacturers choose AGM batteries for this purpose.
It is important to identify vehicles that have AGM batteries. GM supplies this information on their service website. Care must be taken when charging and jump-starting vehicles equipped with these batteries. AGM batteries only like to be charged up to 15 volts. They require a special battery charger. Failure to use the proper charger will reduce the battery’s life and possibly damage it.
When a dead vehicle needs a jump, it is highly recommended to use a jumper box instead of the old-fashioned plug-in charger/jumper, which can reach more than 16 volts in jump mode.
DUAL BATTERY CONTROL MODULE
Auxiliary batteries are found in most GM vehicle applications with Stop/Start technology. If the vehicle has an auxiliary battery, it will have a Dual Battery Control Module (DBCM) (figure 1). The module is mounted near the main service battery and is responsible for keeping components operating when the vehicle is in stop mode in Drive—the auxiliary battery charges when the engine is running. However, if it dies, you must charge and test the battery directly at the terminals. For most late-model GM vehicles, the auxiliary battery is located in the trunk in the left-hand side panel (figure 2).
If an issue is detected with the DBCM, the Stop/Start function will be disabled with possible DTCs.
Problems involving the DBCM include:
- No start, no crank, and no lights on in the dash (the main battery shows full charge).
- DTC P305F (Dual Battery Control Module Performance).
- Blown DBCM fuse(s).
- Poor connections or cable condition.
Care must be taken when replacing or servicing the auxiliary battery. Do not allow the battery positive cable to touch the vehicle. Removing the main battery ground before servicing the auxiliary battery is best.
INTELLIGENT BATTERY SENSOR (B110)
Late-model GM applications also use a sensor to monitor the battery’s charge state. The sensor may have different names like Battery Current Sensor, Battery Monitor Module, or Intelligent Battery Sensor. OEM-generated material called the Intelligent Battery Sensor (IBS) (figure 3). The GM universal part code is B110.
The IBS sensor reports to the BCM on the LIN BUS. It tells the vehicle important 12V information such as state of charge (SOC), voltage, current charge, drain, etc. There are critical 12-volt features that depend on this sensor:
- Battery Maintenance report (OEM, OnStar)
- Enhanced Battery Saver Mode (EBSM)
- Start/Stop System (if equipped)
- Over-the-air (OTA) programming updates
Information from this sensor is shared with other modules and through OnStar-connected maintenance.
SERVICING THE ELECTRICAL SYSTEMS
If the vehicle experiences charging-related concerns or a dead battery, it could result from the sensor going bad. So, it’s good to know what a good sensor looks like! Listed here are some diagnostic aids:
- Unplugging or removing the IBS connector from the negative battery post will reset the learn status. An unlearned IBS will display a state of charge (SOC) error above 95% on the scan tool.
- An excessive battery draw (higher than 250 mA) will prevent the IBS learn from completing successfully in 4 Hrs.
- If the battery state of charge error is more than 10%, then it will disable Stop/Start if equipped, preventing sensor reset.
- It is OK to disconnect the ground cable at the sensor or any point further downstream towards the chassis ground stud.
- DO NOT disconnect IBS from the negative battery post or the connector!
- Unless the 12-volt battery or the sensor is being replaced, the IBS should stay attached to the negative stud with its connector attached at all times.
Late model vehicles with the Stop/ Start system may experience issues with the system not functioning after the battery has been serviced or the negative terminal of the battery was removed. Technicians may observe on a scan tool one or more of the following DTCs set:
- U152D: Body Control Module LIN Bus 9
- P15FF: Battery Monitor Sensor Signal Message Counter Incorrect
- P305D: DC/DC Converter Crank Control Circuit High Voltage
- P305E: DC/DC Converter Crank Control Circuit Low Voltage
- U01B0: Lost Communication with Battery Monitor Module
This condition is usually caused by disconnecting the IBS from the battery’s ground terminal. However, intermittent conditions and poor connections on the LIN Bus may also be a cause. If the IBS is disconnected, it will need to be reset. Use the following procedure:
- Ensure the service and auxiliary batteries (if equipped) are fully charged and all connections are secured.
- Drive the vehicle for at least five minutes.
- Park the vehicle, turn the ignition off, and exit. Ensure that the door closes and the dome light goes out.
- Allow the vehicle to sit undisturbed for at least four hours.
Check your scanned data in the Body Control Module to verify the battery state of charge changed from error 95%. The reading should be the current state of charge learned by the IBS.
Also, if the negative battery terminal was disconnected, check for the proper operation of the OnStar system. If the OnStar display has a RED LED, it must be reset. Contact OnStar with the VIN to place the system back online.
After servicing the electrical system, always verify the OnStar system is functioning. Press the button to make sure an operator answers. If not, the system needs to be reinitialized. Failure to reinitialize the OnStar system may cause the following issues:
- OTA Programming failures.
- Repeat dead battery condition.
- OnStar Module failure requiring a replacement module.
GM vehicles equipped with the Intelligent Battery Sensor (IBS) need special attention when dealing with the following issues:
- Battery recharging
- Battery replacement and servicing
- Electrical system servicing requiring the removal of the ground cable
- IBS replacement or removal
If BCM scan data indicates that the battery SOC is less than 50% of its total capacity (approximately 12.1 volts), the service battery must be charged or replaced. GM recommends cycling the ignition every time after charging a vehicle to reset OnStar’s timeout counter. Without resetting the counter, OnStar will go into sleep mode after 30 days, which prevents battery SOC information from being transmitted to GM. For 2021 and later vehicles, Over-the-Air (OTA) programming updates will be made once the issue is fixed.
Technological advances constantly remind us to be aware of possible procedure changes to the most essential things we do on vehicles. Here at ATRA, we do everything in our power to bring you need-to-know information so you can deliver the goods to your customers seamlessly!
