72bowtieguy

Ok, so I have a 2008 GMC Acadia.....same exact vehicle as the Traverse. The charging system is putting out too much power.

The dashboard is indicating that I need to have the charging system serviced.


The battery is 3 months old.
The alternator belt is a month and a half old.
The alternator is a month and a half old, as well.

Ok, here's what I've found out on my own:
The battery has 12.5 volts when I tested it with engine NOT running.
When I start the engine and test the power, it is at 19.8 volts, which is way too much.

The electrical system can safely operate between 10.5 and 15.5 volts.

There was one OBD code present. I forgot what the code number was, but it indicated that the PCM (computer) was experiencing excessive heat temperatures.

I took the alternator down to a local parts store to have it tested, but thier test machine was not capable of testing it.

Bern

Return the alternator it is defective. It is best to get an alternator from the dealer.

72bowtieguy

Yes, I returned the alternator to the auto parts store for a $160 cash refund. I then went to the dealership and bought one from thier parts department with a price tag of $369.

Obviously the dealer part was more expensive, but I think in the long run, it is money well spent.

Now that the new alternator is installed, the vehicle has no hi or low beam headlights.

All the other lights work properly. I have researched and found that each headlight has its own fuse. (so 4 fuses in all) and one relay controls the hi beams, a separate relay controls the low beams. (so 2 relays in all).

Where is the body control module located?

72bowtieguy

Here's some info I came across (if anyone else is wondering).

Body Control Module (BCM)
The body control module (BCM) is a GMLAN device. It communicates with the engine control module (ECM)
and the instrument panel cluster (IPC) for electrical power management (EPM) operation. The BCM determines
the output of the generator and sends the information to the ECM for control of the generator field control
circuit. It monitors the generator field duty cycle signal circuit information sent from the ECM for control of the
generator. It monitors a battery current sensor, the battery positive voltage circuit, and estimated battery
temperature to determine battery state of charge (SOC). The BCM performs idle boost.

Battery Current Sensor
The battery current sensor is a serviceable component that is connected to the negative battery cable at the
battery. The battery current sensor is a 3-wire hall effect current sensor. The battery current sensor monitors the
battery current. It directly inputs to the BCM. It creates a 5-volt 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.

Engine Control Module (ECM)
The ECM directly controls the generator field control circuit input to the generator. The ECM receives control
decisions based on messages from the BCM. It monitors the generators generator field duty cycle signal circuit
and sends the information to the BCM.

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

Charging System Operation
2009 ENGINE Engine Electrical - Acadia, Enclave, Outlook & Traverse

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 field control circuit. It monitors
the generator performance though the generator field duty cycle signal circuit. The ECM controls the generator
through the generator field control circuit. The signal is a 5-volt 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

The generator provides a feedback signal of the generator voltage output through the generator field duty cycle
signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is a 5-volt
PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. Between
0-5 percent and 100 percent are for diagnostic purposes.

Battery Sulfation Mode
The BCM will enter this mode when the interpreted generator output voltage is less than 13.2 volts 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 kmh (90 mph)
? Current Sensor Fault Exists
? System Voltage was determined to be below 12.56 Volts

When any one of these conditions is met, the system will set targeted generator output voltage to a charging
voltage between 13.9V and 15.5V, 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 SOC 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 and 13.1 volts. 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 and 14.5 volts.

Start Up Mode
When the engine is started the BCM sets a targeted generator output voltage of 14.5 volts 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 volts. The BCM will exit this mode
once the criteria are met for Charge Mode.