Retained Accessory Power System Chevrolet Avalanche I

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Diagnostic Starting Point-Retained Accessory Power

Begin the system diagnosis with the DIAGNOSTIC SYSTEM CHECK-RETAINED ACCESSORY POWER . The Diagnostic System Check will provide the following information

1. Class 2 communication status
2. "U" codes which indicate module communication or circuit failure
3. "B" codes which indicate a possible body function or circuit failure
4. The status of any "U" or "B" codes

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step verifies that the retained accessory power (RAP) power mode function is malfunctioning by checking functions internally enabled by the body control module (BCM).
2. The BCM sends class 2 messages to other control modules via the serial data link, allowing them to operate in RAP power mode. Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
3. This step is analyzing the BCM for DTCs.
4. The presence of DTCs that begin with "U" indicate another module is not communicating. The specified procedure will compile all the available information before tests are performed.

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Important Preliminary Checks Before Starting

1. Perform the «DIAGNOSTIC SYSTEM CHECK-RETAINED ACCESSORY POWER»(/chevrolet/avalanche/i-2001-2006/remont/accessories-control-systems/#retained-accessory-power-system) before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control module(s) can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «RETAINED ACCESSORY POWER (RAP) DESCRIPTION AND OPERATION»(/chevrolet/avalanche/i-2001-2006/remont/accessories-control-systems/#retained-accessory-power-system) .

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the Retained Accessory Power system. Refer to CHECKING AFTERMARKET ACCESSORIES in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «RETAINED ACCESSORY POWER (RAP) ON AFTER TIMEOUT»(/chevrolet/avalanche/i-2001-2006/remont/accessories-control-systems/#retained-accessory-power-system)
2. «RETAINED ACCESSORY POWER (RAP) INOPERATIVE»(/chevrolet/avalanche/i-2001-2006/remont/accessories-control-systems/#retained-accessory-power-system)

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Retained Accessory Power (RAP) Power Mode

Retained accessory power (RAP) is a power mode that permits the operation of selected customer convenience items for 10 minutes after the ignition switch is turned OFF. RAP power mode is enabled by the body control module (BCM).

1. The BCM controls certain body functions.
2. The BCM sends out a class 2 message via the serial data line, which enables/disables other modules at the beginning/end of RAP power mode.

Some BCM features, such as the interior courtesy lamps will function after the 10 minute RAP time limit has elapsed. This is normal, and does not mean RAP power mode is malfunctioning. The BCM enables the following functions in RAP Power Mode

1. The sunroof, if equipped
2. The right and left power rear windows
3. Any class 2 module that functions in RAP power mode, that is not hard-wired, is controlled by the BCM via class 2 power mode messages. EXAMPLE: The Radio will power up if it is turned ON and the BCM transmits a RAP, Run or Accessory message over the class 2 serial data bus.

RAP is disabled when

1. A door is opened.
2. A low battery voltage is detected by the BCM.
3. The transition of ignition switch from OFF to ON or ACC.
4. Ten minutes have elapsed after the ignition was turned OFF.
5. There may be some functions of the vehicle that are hard-wired straight to the battery, these are the exceptions.

The BCM monitors the ignition switch position, battery voltage and passenger compartment door status to determine whether RAP power mode should be enabled. If the ignition switch transitions from ON to OFF, the battery voltage is within the acceptable range and the passenger compartment doors are closed, the BCM enables RAP power mode. After the 10 minutes has elapsed, the BCM sends a class 2 message to the serial data network. This message commands the other modules to stop functioning, that are power mode by the BCM.

Sunroof Relay (If Equipped)

The BCM has a discrete output used for the control of the sunroof relay. In the RAP power mode the BCM will supply a B+ to the control circuit to enable the relay. The BCM also enables the relay in the Accessory and Run power modes. Refer to RETAINED ACCESSORY POWER (RAP) SCHEMATICS to become familiar with the system and for the circuit identification.

See also:
• DIAGNOSTIC SYSTEM CHECK-RETAINED ACCESSORY POWER