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Test Description

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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:  This step is checking for DTCs in the BCM.
  3. 5:  This step is checking for RAP specific DTCs.
Diagnostic System Check - Retained Accessory Power

Step Action Yes No
1 Install a scan tool.
Does the scan tool power up?		 Go to Step 2  Go to SCAN TOOL DOES NOT POWER UP
2 
  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to establish communication with the body control module.
Does the scan tool communicate with the BCM?		 Go to Step 3  Go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE
3
IMPORTANT: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode.
  1. Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool.
  2. Rotate the ignition switch through all positions while observing the Class 2 Power Mode on the Scan Tool. Refer to the Serial Data Power Mode table within the BODY CONTROL SYSTEM DESCRIPTION AND OPERATION , for a list of the power mode states that correspond to each ignition switch position.
Does the Class 2 Power Mode parameter reading match the ignition switch position for all the selected positions?		 Go to Step 4  Go to POWER MODE MISMATCH
4  Select the BCM display DTCs function on the scan tool.
Does the scan tool display any DTCs?		 Go to Step 5  Go to the Symptoms list in the appropriate service category
5  Does the scan tool display B1477 or B1478? Go to Diagnostic Trouble Code (DTC) List  Go to Symptoms - Retained Accessory Power 
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