GM Service Manual Online
For 1990-2009 cars only

Electrical Power Management

The electrical power management (EPM) is used to monitor and control the charging system and alert the driver of possible problems within the charging system. The EPM system makes the most efficient use of the generator output, improves the battery state-of-charge (SOC), extends battery life, and manages system electrical loads.

The load shed operation is a means of reducing electrical loads during a low voltage or low battery SOC condition.

The idle boost operation is a means of improving generator performance during a low voltage or low battery SOC condition.

Each EPM function, either idle boost or load-shed, is discrete. No 2 functions are active at the same time. Idle boost is activated in incremental steps, idle boost 1 must be active before idle boost 2 can be active. The criteria used by the instrument panel module (IPM) to regulate EPM are outlined below:

Function

Battery Temperature Calculation

Battery Voltage Calculation

Amp-hour Calculation

Action Taken

Idle Boost 1 Start

Less Than -15°C (5°F)

Less Than 13 V

--

First level Idle boost requested

Idle Boost 1 Start

--

--

Battery has a net loss greater than 0.6 AH

First level Idle boost requested

Idle Boost 1 Start

--

Less Than 10.9 V

--

First level Idle boost requested

Idle Boost 1 End

Greater Than -15°C (5°F)

Greater Than 12.0 V

Battery has a net loss less than 0.2 AH

First level Idle boost request cancelled

Load Shed 1 Start

--

--

Battery has a net loss of 4.0 AH

Rear Defrost, Heated Mirrors, Heated Seats cycled OFF for 20% of their cycle

Load Shed 1 Start

--

Less Than 10.9 V

--

Rear Defrost, Heated Mirrors, Heated Seats cycled OFF for 20% of their cycle

Load Shed 1 End

--

Greater Than 12.0 V

Battery has a net loss of less than 2.0 AH

Clear Load Shed 1

Idle Boost 2 Start

--

--

Battery has a net loss greater than 1.6 AH

Second level Idle boost requested

Idle Boost 2 Start

--

Less Than 10.9 V

--

Second level Idle boost requested

Idle Boost 2 End

--

Greater Than 12.0 V

Battery has a net loss less than 0.8 AH

Second level Idle boost request cancelled

Idle Boost 3 Start

--

--

Battery has a net loss of 10.0 AH

Third level Idle boost requested

Idle Boost 3 Start

--

Less Than 10.9 V

--

Third level Idle boost requested

Idle Boost 3 End

--

Greater Than 12.0 V

Battery has a net loss of less than 6.0 AH

Third level Idle boost request cancelled

Load Shed 2 Start

--

Less Than 10.9 V

Battery has a net loss greater than 12 AH

Rear Defrost, Heated Mirrors, Heated Seats cycled OFF for 50% of their cycle. The BATTERY SAVER ACTIVE message will be displayed on the DIC

Load Shed 2 Start

--

Less Than 10.9 V

--

Rear Defrost, Heated Mirrors, Heated Seats cycled OFF for 50% of their cycle. The BATTERY SAVER ACTIVE message will be displayed on the DIC

Load Shed 2 End

--

Greater Than 12.6 V

Battery has a net loss of less than 10.5 AH

Clear Load Shed 2

Load Shed 3 Start

--

Less Than 11.9 V

Battery has a net loss greater than 20 AH

Rear Defrost, Heated Mirrors, Heated Seats cycled OFF for 100% of their cycle. The BATTERY SAVER ACTIVE message will be displayed on the DIC

Load Shed 3 End

--

Greater Than 12.6 V

Battery has a net loss of less than 15 AH

Clear Load Shed 3