Retained Accessory Power System Chevrolet Chevy Express H2500

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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. 1. This step verifies that the RAP power mode function is malfunctioning by checking functions internally enabled by the BCM.
2. 3. 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. 5. This step is checking for DTCs in the BCM.
4. 6. The presence of DTCs which begin with "U" indicate that the other module is not communicating. The specified procedure will compile all the available information before tests are performed.

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Scan Tool Output Controls

Scan Tool Output Controls

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Data

Battery Voltage: The scan tool displays the battery system voltage.

Inputs

Accessory Switch: The scan tool display if the ignition switch is in the accessory state or not.

Cargo Door Ajar Switch: Passenger van only. The scan tool displays the position of the cargo door. The scan tool displays On when the door is open.

Driver Door Ajar Sw.: The scan tool displays the position of the driver's door. The scan tool displays On when the door is open.

Passenger Door Ajar Sw.: Passenger van only. The scan tool displays the position of the passenger or the rear door. The scan tool displays On when either door is open.

Run/Crank: The scan tool displays the position of the ignition switch. The scan tool displays On when the ignition switch is in the RUN or CRANK position.

Outputs

RAP Relay: The scan tool displays the commanded state of the WIND RAP relay. Active is displayed when the relay is energized and Inactive is displayed when the relay is de-energized.

Diagnostic Trouble Code (DTC) List

Diagnostic Trouble Code (DTC) List

Circuit Description

The BCM interfaces with the vehicle's power distribution system through the WND RAP relay. The WND RAP relay allows the BCM to control the application of power to the feed circuits of the Power Windows. When the ignition switch is in either the ACC or the ON position, the BCM energizes the WND RAP relay by providing B(+) to the WND RAP relay control circuit.

The BCM turns off the WND RAP relay when the ignition switch is in the START position. The RAP feature therefore disables during engine cranking.

When the ignition switch turns from ON or ACC to OFF, with all of the vehicle doors closed, the BCM leaves the WND RAP relay energized for 10 minutes, or until any vehicle door opens.

Conditions for Running the DTC

The system voltage must be between 9-16 volts.

Conditions for Setting the DTC

1. DTC B1477: The BCM detects a short to ground in the WND RAP relay control circuit when the BCM is trying to energize the WND RAP relay. The condition above must be present for more than 1 second.
2. DTC B1478: The BGM detects a short to battery or an open in the WND RAP relay control circuit when the WND RAP relay is not energized. The condition above must be present for more than 1 second.

Action Taken When the DTC Sets

1. DTC B1477: The BCM stores DTC B1477 in memory. The circuits powered by the WND RAP relay will not operate.
2. DTC B1478: The BCM stores DTC B1478 in memory. The circuits powered by the WND RAP relay remain powered at all times if the relay control circuit is shorted to battery. The circuits powered by the WND RAP relay will never be powered if the relay control circuit is open.

Conditions for Clearing the DTC

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids

If the DTC B1477 or B1478 is a history DTC, the fault may be intermittent. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS .

The following conditions may cause an intermittent malfunction to occur

1. An intermittent short to ground or to battery in the WND RAP relay control circuit.
2. The WND RAP relay coil is shorted to ground or to battery internally.
3. The BCM is shorted to ground or to battery internally.

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

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1. 2. During the WND RAP relay operation, listen for an audible click. Command the ON and the OFF states. Repeat the commands as necessary.
2. 3. Verifies whether the WND RAP relay has a defect.
3. 4. Tests the control circuit of the WND RAP relay.
4. 5. Tests the ground circuit of the WND RAP relay.

Important Preliminary Checks Before Starting

1. Perform the «Diagnostic System Check - Retained Accessory Power»(/chevrolet/chevy-express-h2500/2003-2003/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/chevy-express-h2500/2003-2003/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»(/chevrolet/chevy-express-h2500/2003-2003/remont/electrical-component-locations/#wiring-systems-general-information__checking-aftermarket-accessories) .
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 .

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/chevy-express-h2500/2003-2003/remont/accessories-control-systems/#retained-accessory-power-system)
2. «Retained Accessory Power (RAP) Inoperative»(/chevrolet/chevy-express-h2500/2003-2003/remont/accessories-control-systems/#retained-accessory-power-system)

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Retained Accessory Power (RAP) Power Mode

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 BCM.

The BCM

1. Controls certain body functions.
2. 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 right and left power windows through the WND RAP relay.
2. 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 works in RAP power mode due to the BCM allowing and controlling it.

RAP is disabled when

1. The 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. 10 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 moded by the BCM.

WND RAP Relay

The BCM controls the WND RAP relay's coil circuit using high side drive. The output of the relay is used to supply B+ to the Power Windows. The WND RAP relay also acts as the Power Windows switched Accessory supply when the Accessory power mode is selected.

See also:
• TESTING FOR INTERMITTENT AND POOR CONNECTIONS
• CHECKING AFTERMARKET ACCESSORIES
• Diagnostic System Check - Retained Accessory Power