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2 Posts
Discussion Starter #1
Is it normal for the battery voltage to read 15v or 15.1v?

I've never had this until recently. Usually the battery voltage sits between 12 and 14.

9,940 Posts
Is the car running at the time. Normal with car off is 12.6, and while running about 14.5 . Either way, too high. How accurate is your gauge?

2 Posts
Discussion Starter #3
I don't know how accurate the guage is. Today running it was a steady14.5v. Starting up it was 13.8v. What does the high voltage mean? Alternator problem or voltage regulator problem?

208 Posts
Mine is frequently at 15-15.3 volts while driving.. 12.7 at rest and 13.8 at idle.. I've given up trying to figure out the charging alogrithim

1,231 Posts
Service Information
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2007 Chevrolet Equinox | Equinox, Torrent VIN L Service Manual | Document ID: 1808940

Charging System Description and Operation

Electrical Power Management (EPM) Overview
The electrical power management (EPM) system is designed tomonitor and control the charging system and send diagnosticmessages to alert the driver of possible problems with the batteryand generator. This EPM system primarily utilizes existing on-boardcomputer capability to maximize the effectiveness of the generator,to manage the load, improve battery state-of-charge and life, andminimize the system's impact on fuel economy. The EPM systemperforms 3 functions:
•It monitors the battery voltage and estimates the batterycondition.
•It takes corrective actions by boosting idle speeds, andadjusting the regulated voltage.
•It performs diagnostics and driver notification.

The battery condition is estimated during ignition-off andduring ignition-on. During ignition-off the state-of-charge (SOC)of the battery is determined by measuring the open-circuit voltage.The SOC is a function of the acid concentration and the internalresistance of the battery, and is estimated by reading the batteryopen circuit voltage when the battery has been at rest for severalhours.

The SOC can be used as a diagnostic tool to tell the customeror the dealer the condition of the battery. Throughout ignition-on,the algorithm continuously estimates SOC based on adjusted net amphours, battery capacity, initial SOC, and temperature.

While running, the battery degree of discharge is primarilydetermined by a battery current sensor, which is integrated toobtain net amp hours.

In addition, the EPM function is designed to performregulated voltage control (RVC) to improve battery SOC, batterylife, and fuel economy. This is accomplished by using knowledge ofthe battery SOC and temperature to set the charging voltage to anoptimum battery voltage level for recharging without detriment tobattery life.

The Charging System Description and Operation is divided into3 sections. The first section describes the chargingsystem components and their integration into the EPM. The secondsection describes charging system operation. The third sectiondescribes the instrument panel cluster (IPC) operation of thecharge indicator, driver information center (DIC) messages, andvoltmeter operation.
Charging System Components

The generator is a serviceable component. If there is adiagnosed failure of the generator it must be replaced as anassembly. The engine drive belt drives the generator. When therotor is spun it induces an alternating current (AC) into thestator windings. The AC voltage is then sent through a series ofdiodes for rectification. The rectified voltage has been convertedinto a direct current (DC) for use by the vehicles electricalsystem to maintain electrical loads and the battery charge. Thevoltage regulator integral to the generator controls the output ofthe generator. It is not serviceable. The voltage regulatorcontrols the amount of current provided to the rotor. If thegenerator has field control circuit failure, the generator defaultsto an output voltage of 13.8 volts.

Body Control Module (BCM)

The body control module (BCM) is a GMLAN device. Itcommunicates with the engine control module (ECM) and theinstrument panel cluster (IPC) for electrical power management(EPM) operation. The BCM determines the output of the generator andsends the information to the ECM for control of the generator fieldcontrol circuit. It monitors the generator field duty cycle signalcircuit information sent from the ECM for control of the generator.It monitors a battery current sensor, the battery positive voltagecircuit, and estimated battery temperature to determine batterystate of charge (SOC). The BCM sends idle boost requests to theECM.

Battery Current Sensor

The battery current sensor is a serviceable component that isconnected to the negative battery cable at the battery. The batterycurrent sensor is a 3-wire hall effect current sensor. The batterycurrent sensor monitors the battery current. It directly inputs tothe BCM. It creates a 5-volt pulse width modulation (PWM) signal of128 Hz with a duty cycle of0–100 percent. Normal duty cycle is between5–95 percent. Between0–5 percent and95–100 percent are for diagnosticpurposes.

Engine Control Module (ECM)

The ECM directly controls the generator field control circuitinput to the generator. The ECM receives control decisions based onmessages from the BCM. It monitors the generators generator fieldduty cycle signal circuit and sends the information to theBCM.

Instrument Panel Cluster (IPC)

The IPC provides a means of customer notification in case ofa failure and a voltmeter. There are 2 means ofnotification, a charge indicator and a driver information center(DIC) message of SERVICE BATTERY CHARGING SYSTEM.

Charging System Operation
The purpose of the charging system is to maintain the batterycharge and vehicle loads. There are 6 modes of operationand they include:
•Battery Sulfation Mode
•Charge Mode
•Fuel Economy Mode
•Headlamp Mode
•Start Up Mode
•Voltage Reduction Mode

The engine control module (ECM) controls the generatorthrough the generator turn on signal. It monitors the generatorperformance though the generator field duty cycle signal circuit.The signal is a 5-volt pulse width modulation (PWM) signal of128 Hz with a duty cycle of0–100 percent. Normal duty cycle is between5–95 percent. Between0–5 percent and95–100 percent are for diagnostic purposes.The following table shows the commanded duty cycle and outputvoltage of the generator:

Commanded Duty Cycle

Generator Output Voltage


11 V


11.56 V


12.12 V


12.68 V


13.25 V


13.81 V


14.37 V


14.94 V


15.5 V

The generator provides a feedback signal of the generatorvoltage output through the generator field duty cycle signalcircuit to the ECM. This information is sent to the body controlmodule (BCM). The signal is a 5-volt PWM signal of128 Hz with a duty cycle of0–100 percent. Normal duty cycle is between5–99 percent. Between0–5 percent and 100 percent are fordiagnostic purposes.
Battery Sulfation Mode
The BCM will enter this mode when the interpreted generatoroutput voltage is less than 13.2 volts for 45 minutes. When thiscondition exists the BCM will enter Charge Mode for 2–3minutes. The BCM will then determine which mode to enter dependingon voltage requirements.
Charge Mode
The BCM will enter Charge Mode when ever one of the followingconditions are met.
•The wipers are ON for more than 3 seconds.
•GMLAN (Climate Control Voltage Boost Mode Request) is true,as sensed by the HVAC control head. High speed cooling fan, reardefogger and HVAC high speed blower operation can cause the BCM toenter the Charge Mode.
•The estimated battery temperature is less than 0°C(32°F).
•Battery State of Charge is less than 80 percent.
•Vehicle Speed is greater than 145 kph (90 mph)
•Current Sensor Fault Exists
•System Voltage was determined to be below 12.56 volts
•Tow/Haul Mode is enabled

When any one of these conditions is met, the system will settargeted generator output voltage to a charging voltage between13.9–15.5 volts, depending on the battery state of chargeand estimated battery temperature.
Fuel Economy Mode
The BCM will enter Fuel Economy Mode when the ambient airtemperature is at least 0°C (32°F) but less than orequal to 80°C (176°F), the calculated batterycurrent is less than 15 amps and greater than −8 amps,and the battery state of charge (SOC) is greater than or equal to80 percent. Its targeted generator output voltage is the opencircuit voltage of the battery and can be between12.5–13.1 volts. The BCM will exit this mode and enterCharge Mode when any of the conditions described above arepresent.
Headlamp Mode
The BCM will enter Headlamp Mode when ever the headlamps areON (high or low beams). Voltage will be regulated between13.9–14.5 volts
Start Up Mode
When the engine is started the BCM sets a targeted generatoroutput voltage of 14.3 volts for 30 seconds.
Voltage Reduction Mode
The BCM will enter Voltage Reduction Mode when the calculatedbattery temperature is above 0°C (32°F). Thecalculated battery current is less than 1 amp andgreater than −7 amps, and the generator fieldduty cycle is less than 99 percent. Its targetedgenerator output voltage is 13 volts. The BCM will exitthis mode once the criteria are met for Charge Mode.
Instrument Panel Cluster (IPC) Operation
Charge Indicator Operation

The instrument panel cluster (IPC) illuminates the chargeindicator and displays a warning message in the driver informationcenter (DIC) when the one or more of the following occurs:

•The engine control module (ECM) detects that the generatoroutput is less than 11 volts or greater than16 volts. The IPC receives a GMLAN message from the ECMrequesting illumination.
•The BCM determines that the system voltage is less than11 volts or greater than 16 volts.
•The IPC receives a GMLAN message from the body control module(BCM) indicating there is a system voltage range concern.
•The IPC performs the displays test at the start of eachignition cycle. The indicator illuminates for approximately3 seconds.
•The ignition is ON, with the engine OFF.

Battery Voltage

The IPC displays the system voltage as received from the BCMover the GMLAN serial data circuit. If there is no communicationwith the BCM then the gauge will indicate minimum.


The BCM and the ECM will send a GMLAN message to the DIC forthe SERVICE BATTERY CHARGING SYSTEM message to be displayed. It iscommanded ON when a charging system DTC is a current DTC. Themessage is turned OFF when the conditions for clearing the DTC havebeen met.
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