obermd-
With the battery current sensor that's part of the Cruze, and the Alternator charging strategy based on outside temperature I've seen similar things every fall/winter.
I pulled the battery last fall and had it load tested. Thinking that out of the car would give a better reading since the Cruze has an interesting charging behavior. It checked out fine.
Loose cables are the only time I seen a voltage >15V. You may want to remove and reinstall the cables.
Charging System Operation
The purpose of the charging system is to maintain the battery charge and vehicle
loads. There are 6 modes of operation and 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 generator through the generator
turn ON signal circuit. The ECM monitors the generator performance though the
generator field duty cycle signal circuit. The signal is a pulse width modulation
(PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is
between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic
purposes. The following table shows the commanded duty cycle and output
voltage of the generator:
Battery Sulfation Mode
The BCM will enter this mode when the interpreted generator output voltage is
less than 13.2 V for 45 minutes. When this condition exists the BCM will enter
Charge Mode for 2-3 minutes. The BCM will then determine which mode to enter
depending on voltage requirements.
Charge Mode
The BCM will enter Charge Mode when ever one of the following conditions are
met.
The wipers are ON for than 3 seconds.
GMLAN (Climate Control Voltage Boost Mode Request) is true, as sensed
by the HVAC control head. High speed cooling fan, rear defogger and HVAC
high speed blower operation can cause the BCM to enter 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 km/h (90 mph)
Current sensor fault exists.
System voltage was determined to be below 12.56 V
When any one of these conditions is met, the system will set targeted generator
output voltage to a charging voltage between 13.9-15.5 V, depending on the battery
state of charge and estimated battery temperature.
Fuel Economy Mode
The BCM will enter Fuel Economy Mode when the estimated battery temperature is
at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery
current is less than 15 amperes and greater than -8 amperes, and the battery
state-of-charge is greater than or equal to 80 percent. Its targeted generator
output voltage is the open circuit voltage of the battery and can be between 12.5-
13.1 V. The BCM will exit this mode and enter Charge Mode when any of the
conditions described above are present.
Headlamp Mode
The BCM will enter Headlamp Mode when ever the headlamps are ON (high or
low beams). Voltage will be regulated between 13.9-14.5 V.
Start Up Mode
When the engine is started the BCM sets a targeted generator output voltage of
14.5 V for 30 seconds.
Voltage Reduction Mode
The BCM will enter Voltage Reduction Mode when the calculated ambient air
temperature is above 0°C (32°F). The calculated battery current is less than 1
ampere and greater than -7 amperes, and the generator field duty cycle is less
than 99 percent. Its targeted generator output voltage is 12.9 V. The BCM will exit
this mode once the criteria are met for Charge Mode.
Instrument Panel Cluster Operation
Charge Indicator Operation
The instrument panel cluster illuminates the charge indicator and displays a
warning message in the driver information center if equipped, when the one or
more of the following occurs:
The engine control module (ECM) detects that the generator output is less
than 11 V or greater than 16 V. The instrument panel cluster receives a
GMLAN message from the ECM requesting illumination.
The instrument panel cluster determines that the system voltage is less than
11 V or greater than 16 V for more than 30 seconds. The instrument panel
cluster receives a GMLAN message from the body control module (BCM)
indicating there is a system voltage range concern.
The instrument panel cluster performs the displays test at the start of each
ignition cycle. The indicator illuminates for approximately 3 seconds.
BATTERY NOT CHARGING SERVICE CHARGING SYSTEM
The BCM and the ECM will send a GMLAN message to the driver information
center for the BATTERY NOT CHARGING SERVICE CHARGING SYSTEM
message to be displayed. It is commanded ON when a charging system DTC is a
current DTC. The message is turned OFF when the conditions for clearing the
DTC have been met.
SERVICE BATTERY CHARGING SYSTEM
The BCM and the ECM will send a GMLAN message to the driver information
center for the SERVICE BATTERY CHARGING SYSTEM message to be displayed.
It is commanded ON when a charging system DTC is a current DTC. The
message is turned OFF when the conditions for clearing the DTC have been met.