Test Description

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

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.
4: This step is checking for DTCs in the BCM.
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	Turn ON the ignition, with the engine OFF. 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. Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool. 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