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Test Description

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

  1. 4:  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. 5:  The symptom list in Symptoms will determine the correct diagnostic procedure to use.
  3. 6:  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.
Diagnostic System Check - Engine Electrical

Step Action Yes No
1 Did you perform the Battery Inspection/Test? Go to Step 2  Go to Battery Inspection/Test (Non-HP2) 
2 Install a scan tool.
Does the scan tool power up?		 Go to Step 4  Go to Scan Tool Does Not Power Up
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 in Body Control Systems, 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 in Body Control System
4 
  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to communicate with each module on the class 2 serial data circuit.

    If using a Tech 2, obtain this information using the class 2 Message Monitor feature.

Does the scan tool communicate with any module on the class 2 serial data circuit?		 Go to Step 5  Go to Scan Tool Does Not Communicate with Class 2 Device
5 
  1. Select the Display DTCs function for each module.

    If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules have DTCs set.

  2. Record all of the displayed DTCs the DTC status and the module which set the DTC.
Does the scan tool display any DTCs?		 Go to Step 6  Go to Symptoms - Engine Electrical 
6  Does the scan tool display any DTC beginning with "U"? Go to Diagnostic Trouble Code (DTC) List Go to Step 7 
7 Does the scan tool display any DTC beginning with "P"? Go to Diagnostic Trouble Code (DTC) List 4.8 L, 5.3 L, 6.0 L or Diagnostic Trouble Code (DTC) List 8.1 L in Engine Controls Go to Step 8 
8 Does the scan tool display any DTC beginning with "B"? Go to Diagnostic Trouble Code (DTC) List Go to Diagnostic Trouble Code (DTC) List 
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