Retained Accessory Power Buick Century VI

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Begin the system diagnosis with a DIAGNOSTIC SYSTEM CHECK - RETAINED ACCESSORY POWER .

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

Test Description

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

1. 2. 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.
2. 4. The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.

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Scan Tool Data Definitions

Accessory 1: Input from ignition switch ACCESSORY circuit. Used to determine power mode. Hot in ACCESSORY and RUN.

Door Jamb Switch: Input showing state of the passenger doors.

Driver Door Switch: Input from the driver door indicating door status.

Ignition 0: Input to the control module from the ignition switch indicating the Ignition 0 position.

Switch closed (HOT) in ignition switch positions Unlock, Accessory, Run, Crank.

Ignition 1: Input to the control module from the ignition switch indicating the ignition 1 position. Switch closed (HOT) in ignition switch positions Run, Crank.

RAP Output: Output indicates state that the control module has commanded.

Trunk Ajar Switch: Indicates state of switch used to control lamp in trunk and IPC indicator.

Diagnostic Trouble Code (DTC) List

Diagnostic Trouble Code (DTC) List

Circuit Description

The BCM interfaces with the vehicle's power distribution system through the RAP relay. The RAP relay allows the BCM to control the application of power to the feed circuits of the Sunroof and power windows. When the ignition switch is in either the ACC or the RUN position, the BCM energizes the RAP relay by grounding the RAP relay control circuit.

The BCM turns off the 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 to LOCK or OFF, with all of the vehicle doors closed, the BCM leaves the RAP relay energized for 10 minutes, or until any vehicle door opens and the BCM detects a ground signal in one of the door ajar circuits.

Conditions for Setting the DTC

1. The BCM detects no voltage at the RAP relay control circuit when the BCM has not grounded the circuit.
2. The conditions above must be present for more than 300 milliseconds.

Action Taken When the DTC Sets

1. The BCM stores DTC B1477 in memory.
2. The circuits powered by the RAP relay remain powered at all times if the relay control circuit is shorted to ground.
3. The circuits powered by the RAP relay will never be powered if the relay control circuit is open.

Conditions for Clearing the DTC

1. The correct voltage is present at the RAP relay control circuit as detected by the BCM.
2. A history DTC B1477 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

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

1. 2. Listen for an audible click when the RAP relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. 3. This step tests for voltage at the coil side of the RAP relay. The INADV POWER BUS fuse supplies power to the coil side of the RAP relay.
3. 4. This step verifies that the Body Control Module (BCM) is providing ground to the RAP relay.
4. 5. This step tests if ground is constantly being applied to the RAP relay.

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The Body Control Module (BCM) interfaces with the vehicle's power distribution system through the RAP relay. The RAP relay allows the BCM to control the application of power to the feed circuits of the Sun-roof and the power windows. When the ignition switch is in either the ACC or the RUN position, the BCM energizes the RAP relay by grounding the RAP relay control circuit.

The BCM turns off the 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 ACCESSORY to UNLOCK or OFF, with all of the vehicle doors closed, the BCM leaves the RAP relay energized for 10 minutes, or until any vehicle door opens and the BCM detects a ground signal in one of the door ajar circuits.

Conditions for Running the DTC

The BCM must be commanding the RAP relay to energize.

1. The BCM detects a short to battery in the RAP relay control circuit when the BCM is trying to energize the RAP relay.
2. The condition above must be present for more than 300 milliseconds.

1. The RAP relay powered functions will not operate
2. The BCM stores DTC B1478 in memory.

1. A current DTC B1478 will clear if the short to battery in the RAP relay control circuit is no longer detected by the BCM when the RAP relay is commanded to energize.
2. A history DTC B1478 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

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

1. 2. Listen for an audible click when the RAP relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. 3. This step verifies that the Body Control Module (BCM) is providing ground to the RAP relay.

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Visual/Physical Inspection

1. Inspect for aftermarket devices which may 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 may 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»(/buick/century/vi-1997-2005/remont/accessories-control-systems/#retained-accessory-power)
2. «Retained Accessory Power (RAP) Inoperative»(/buick/century/vi-1997-2005/remont/accessories-control-systems/#retained-accessory-power)

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The modules listed below all receive a RAP message from the Body Control Module (BCM) over the serial data circuits. The BCM monitors the ignition switch position, battery condition and passenger compartment door status to determine whether RAP should be initiated. The BCM then sends a message to the listed modules telling them that they are in RAP power mode. The modules then support the operation of the systems under their control as required by their RAP power mode strategy.

RAP will end when one of the following conditions are met

1. The BCM receives a hardwired input indicating the opening of a passenger compartment door.
2. The BCM receives a message from its internal timer indicating the end of the RAP period after 10 minutes.
3. The BCM detects a decrease in battery capacity below a prescribed limit.

The BCM then sends a serial data message to the listed modules ending the RAP function.

The modules receiving serial data messages for RAP functions are

1. Vehicle Interface Unit (VIU) (if equipped)
2. Instrument Panel Cluster (IPC)
3. HVAC Control Module (w/CJ2)

When the body control module (BCM) is in the RAP function as described above, it closes the RAP relay. This provides power during the RAP period for the following

1. Sunroof
2. Power Windows
3. Radio

The BCM opens the RAP relay to end the RAP function when it ends the RAP function as outlined in the previous text.

See also:
• DIAGNOSTIC SYSTEM CHECK - RETAINED ACCESSORY POWER