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Home >> Cadillac >> 2007 >> STS V >> Repair and Diagnosis >> External Pages >> Different car >> Section 11 (Computer/Integrating Systems) >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with High Speed GMLAN Device >> Test Description

Test Description

WARNING: This page is about a different car, the 2006 Cadillac STS. 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 malfunction in the high speed GMLAN serial data circuits uses a different procedure from a total malfunction of the high speed GMLAN data circuits. The scan tool communicates with the following modules on the high speed GMLAN serial data circuits:
    • Distance sensing cruise control (DSCC) module
    • Instrument panel module (IPM)
    • Electronic brake control module (EBCM)
    • Electronic suspension control (ESC) module
    • Engine control module (ECM)
    • Transmission control module (TCM)
  2. 8:  Data link connector (DLC) terminals 6 and 14 provide the connection to the GMLAN serial data high circuit and the GMLAN serial data low circuit respectively.
  3. 15:  If only one of the high speed GMLAN circuits is open all communication on the high speed bus will be disrupted.
  4. 19:  The communication malfunction may have prevented diagnosis of the customer complaint.
Scan Tool Does Not Communicate with High Speed GMLAN Device

Step Action Yes No
Schematic Reference: Data Link Connector Schematics 
Connector End View Reference: Master Electrical Component List
1 Did you perform the Diagnostic System Check - Vehicle? Go to Step 2  Go to Diagnostic System Check - Vehicle
2 
IMPORTANT: Make sure the CANdi module works fine. When functioning properly, CANdi's LED flashes. In the event of a problem, the LED will be constantly illuminated.
  1. Turn ON the ignition, with the engine OFF.
  2. Perform the Vehicle DTC Information function on the scan tool, under Computer/Integrating Systems.
Does the scan tool communicate with any module on the GMLAN serial data circuits?		 Go to Step 3  Go to Step 6 
3 Did you record any DTCs in the range of U2105-U2199? Go to DTC U2105-U2199  Go to Step 4 
4 Did you record any DTCs in the range of U0100-U0299? Go to DTC U0100-U0299  Go to Step 5 
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.
  1. Disconnect the scan tool from the data link connector (DLC).
  2. Test the high speed GMLAN serial data circuits for:
    • An intermittent short to ground
    • An intermittent short to voltage
    • An intermittent short between them
    • An intermittent open on any of the circuits
Refer to the following procedures:Did you find and correct the condition?		 Go to Step 21  Go to Diagnostic Aids
6
  1. Disconnect the instrument panel module (IPM).
  2. Test the following circuits of the IPM for an open or short to ground:
    • The battery positive voltage input circuits
    • The battery positive voltage output circuits
    • The ignition mode switch input circuits
    • The switched battery positive voltage circuits
Refer to Circuit Testing and Wiring Repairs .Did you find and correct the condition?		 Go to Step 18  Go to Step 7 
7 Test the ground circuits of the IPM for an open. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 18  Go to Step 8 
8  Inspect for poor connections at the DLC terminals 6 and 14. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 Go to Step 18  Go to Step 9 
9 Test the high speed GMLAN serial data circuits between the IPM and DLC for:
  • A short to ground
  • A short to battery
  • A short between them
  • An open

Refer to the following procedures:
Did you find and correct the condition?		 Go to Step 18  Go to Step 10 
10
  1. Reconnect the IPM.
  2. Disconnect the farthest module from the DLC that is connected to high speed GMLAN serial data circuits. Refer to Data Link Connector Schematics .
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with the IPM.
Does the scan tool communicate with the IPM?		 Go to Step 15  Go to Step 11 
11
  1. Turn OFF the ignition.
  2. Disconnect the farthest module from the DLC that is still connected to high speed GMLAN serial data circuits. Refer to Data Link Connector Schematics .
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with the IPM.
Does the scan tool communicate with the IPM?		 Go to Step 12  Go to Step 13 
12 Test the high speed GMLAN serial data circuits between the last 2 disconnected modules for:
  • A short to ground
  • A short to battery
  • A short between them
  • An open

Refer to the following procedures:
Did you find and correct the condition?		 Go to Step 18  Go to Step 15 
13 Is the IPM the last module still connected to high speed GMLAN data circuits? Go to Step 14  Go to Step 11 
14
  1. Turn OFF the ignition.
  2. Disconnect the IPM.
  3. Test the high speed GMLAN serial data circuits between IPM and the previous disconnected module for:
    • A short to ground
    • A short to battery
    • A short between them
    • An open
Refer to the following procedures:Did you find and correct the condition?		 Go to Step 18  Go to Step 16 
15  Test each of the high speed GMLAN circuits of the last disconnected module to the next module closer to DLC for an open. Refer to the following procedures:
Did you find and correct the condition?		 Go to Step 18  Go to Step 16 
16 Inspect for poor connections at the high speed GMLAN serial data circuits of the suspected module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 Go to Step 18  Go to Step 17 
17 Replace the suspected module. Refer to Control Module References  for replacement, setup, and programming.
Did you complete the replacement?		 Go to Step 18  -
18
  1. Reconnect all of the disconnected modules.
  2. Install a scan tool.
  3. Turn ON the ignition, with the engine OFF.
  4. Select the Display DTCs function for each module.
  5. Record all of the displayed DTCs and the DTC status.
Did you record any DTCs which begin with a "U" and with a current status?		 Go to Diagnostic Trouble Code (DTC) List - Vehicle Go to Step 19 
19  Did you record any DTCs which do not begin with a "U"? Go to Diagnostic Trouble Code (DTC) List - Vehicle Go to Step 20 
20 Did you diagnose all of the DTCs? Go to Step 21  Go to Step 18 
21 Use the scan tool in order to clear the DTCs.
Did you complete the action?		 System OK -
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