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Test Description

WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 2:  A partial loss of communication in the class 2 serial data circuit uses a different procedure than a total loss of communication of the class 2 serial data circuit.
  2. 4:  The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition.
    • U1300
    • U1301
    • U1305
  3. 6:  A State of Health DTC with a history status may be present along with a U1000 or U1255 with a current status. This indicates that the malfunction occurred when the ignition was on.
  4. 10:  Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
  5. 12:  Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
  6. 13:  Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
  7. 19:  If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
  8. 20:  The communication concern may have prevented diagnosis of the customer complaint.
Scan Tool Does Not Communicate with Class 2 Device

Step Action Yes No
Schematic Reference:  Data Link Connector (DLC) Schematics  
Connector End View Reference:  Master Electrical Component List 
1 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 communicate with each module on the class 2 serial data circuit.
Does the scan tool communicate with any module on the class 2 serial data circuit?		 Go to Step 3  Go to Step 8 
3
  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 do have DTCs set.
  2. Record all of the displayed DTCs, the DTC status and the module which set the DTC.
Did you record any DTCs in the range of U1000 to U1305?		 Go to Step 4  Go to Step 7 
4  Are history DTCs U1300, U1301 or U1305 retrieved from any module? Go to Step 5  Go to Step 6 
5
IMPORTANT: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions.
Test the class 2 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following in Wiring Systems:Did you find and correct the condition?		 Go to Step 18  Go to Step 6 
6  Are U1000 or U1255 the only DTCs displayed in the previously specified range? Go to DTC U1000 and U1255  Go to DTC U1001-U1254 
7 Diagnose the non communicating module by using the DTC U1001-U1254 Lost Communications with XXX procedure for the module which is not communicating. The DTC U1001-U1254 Lost Communications with XXX procedure will determine which module is not communicating. Refer to DTC U1001-U1254 .
Did you complete the action?		 Go to Control Module References in Body Control System for the applicable Diagnostic System Check -
8
  1. Turn OFF the ignition.
  2. Disconnect the scan tool from the data link connector (DLC).
  3. Inspect for poor connections and terminal tension at the DLC. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Control Module References in Body Control System for the applicable Diagnostic System Check Go to Step 9 
9 Test the signal ground circuits of the DLC for an open or high resistance. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Control Module References in Body Control System for the applicable Diagnostic System Check Go to Step 10 
10 
  1. Isolate the power mode master (PMM) module from all other modules on the class 2 serial data circuit. To identify which module is the PMM, refer to Body Control System Description and Operation in Body Control System.
  2. Attempt to communicate with the PMM.
Does the scan tool communicate with the PMM?		 Go to Step 12  Go to Step 11 
11
  1. Test the class 2 serial data circuit between the DLC and the PMM for the following conditions. Turn ON the ignition when testing for a short to voltage:
    • High resistance
    • Open
    • Short to ground
    • Short to voltage
  2. Test the following circuits of the PMM for an open or high resistance:
    • The battery positive voltage input circuits
    • The battery positive voltage output circuits
    • The ignition voltage input circuits
    • The ignition voltage output circuits
    • The switched battery positive voltage supply circuits
    • The ground circuits
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.Did you find and correct the condition?		 Go to Step 18  Go to Step 16 
12 
IMPORTANT: The PMM must remain connected to the DLC. Use the appropriate jumper if needed.
  1. Turn OFF the ignition.
  2. Connect any previously disconnected modules.
  3. Disconnect the splice pack which connects the modules to the class 2 serial data circuit, by removing the splice pack comb.
  4. Turn ON the ignition, with the engine OFF.
  5. Attempt to communicate with any module still connected to the class 2 serial data circuit after disconnecting the splice pack.
Does the scan tool communicate with any module still connected to the class 2 serial data circuit after the splice pack was disconnected?		 Go to Step 13  Go to Step 14 
13 
IMPORTANT: The PMM must remain connected to the DLC. Use the appropriate jumper if needed.
Using the appropriate jumper at the splice pack, perform the following in order to determine which class 2 serial data circuit or module is causing the concern:
  1. Turn ON the ignition, with the engine OFF.
  2. Using the appropriate jumper, connect each previously disconnected module to the class 2 serial data circuit one at a time until communication with the class 2 serial data circuit is lost.
Did you complete the action?		 Go to Step 15  -
14 Repair short to ground or voltage condition in the class 2 serial data circuits or in-line connectors to the last module connected in the branch being diagnosed. Refer to Wiring Repairs and Connector Repairs in Wiring Systems
Did you complete the repair?		 Go to Step 18  -
15 Test the class 2 serial data circuits to the suspect module for a short to ground or a short to voltage
Turn ON the ignition with the engine OFF when testing for a short to voltage.
Refer to Circuit Testing and Wiring Repairs in Wiring Systems
Did you find and correct the condition?		 Go to Step 18  Go to Step 16 
16 Inspect for poor connections and terminal tension at the harness connector of the suspect module. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 18  Go to Step 17 
17
IMPORTANT: Perform the module setup procedure if required. Refer to
Replace the suspect module. Refer to Control Module References in Body Control System for the appropriate Repair Instructions for module replacement.Did you complete the replacement?		 Go to Step 18  -
18
  1. Connect all of the modules.
  2. Connect all the connectors.
  3. Install a scan tool.
  4. Turn ON the ignition leaving the engine OFF.
    5. IMPORTANT: The scan tool may require a power up reset before communication will occur due to a short on the class 2 serial data circuit. Turn off or disconnect the scan tool before you display DTCs.
  5. Wait for 10 seconds.
  6. 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 do have DTCs set.
  7. Record all of the displayed DTCs and the DTC status.
Did your record any DTCs which begin with a letter "U" and with a current status?		 Go to Step 20  Go to Step 19 
19  Did you record any DTCs which do not begin with a letter "U"? Go to Step 20  Go to Step 21 
20  Diagnose the DTCs as directed by the diagnostic procedures for the particular module or concern.
Did you complete the action?		 Go to Step 21  -
21 Did you diagnose all of the DTCs? Go to Step 22  Go to Step 20 
22 Clear the DTCs using the scan tool.
Did you complete the action?		 Go to Control Module References in Body Control System for the applicable Diagnostic System Check -
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