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Home >> Cadillac >> 2006 >> STS V >> Repair and Diagnosis >> External Pages >> Different car >> Section 17 (Data Communication System) >> 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 2007 Cadillac CTS. 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 following modules communicate on the high speed GMLAN serial data circuits:
    • Engine control module (ECM)
    • Transmission control module (TCM)
  2. 7:  Data link connector terminals 6 and 14 provide the connection to the GMLAN serial data high circuit and the GMLAN serial data low circuit respectively.
  3. 14:  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 Communication 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. Attempt to communicate with the modules on high speed GMLAN.
Does the scan tool communicate with any module on the GMLAN serial data circuits?		 Go to Step 3  Go to Step 7 
3 Did you record any DTCs in the range of U0100 to U0299? Go to DTC U0100-U0299  Go to Step 4 
4 Did you record DTC U0001, with a history status? 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.
  1. Disconnect the scan tool from the data link connector (DLC).
  2. Test the high speed GMLAN serial data circuits for the following conditions:
    • 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 16  Go to Diagnostic Aids
6 Diagnose the non-communicating module by using the DTC U0100-U0299 procedure for the module which is not communicating. Refer to DTC U0100-U0299 .
Did you complete the action?		 Go to Diagnostic System Check - Vehicle -
7 
  1. Disconnect the scan tool.
  2. 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 16  Go to Step 8 
8
  1. Disconnect the engine control module (ECM).
  2. Turn ON the ignition, with the engine OFF.
  3. Attempt to communicate with the transmission control module (TCM).
Does the scan tool communicate with the TCM?		 Go to Step 11  Go to Step 9 
9
  1. Turn OFF the ignition.
  2. Disconnect the TCM.
  3. Test the high speed GMLAN serial data circuits between the TCM and ECM for the following conditions:
    • A short to ground
    • A short to battery
    • A short between high speed GMLAN (+) and high speed GMLAN (-)
    • An open
Refer to the following procedures:Did you find and correct the condition?		 Go to Step 13  Go to Step 10 
10 Test the high speed GMLAN serial data circuits between the TCM and DLC for the following conditions:
  • A short to ground
  • A short to battery
  • A short between high speed GMLAN (+) and high speed GMLAN (-)

Refer to the following procedures:
Did you find and correct the condition?		 Go to Step 13  Go to Step 11 
11 Inspect for poor connections at the high speed GMLAN serial data circuits of the last disconnected module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 Go to Step 13  Go to Step 12 
12 Replace the last disconnected module. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?		 Go to Step 13  -
13
  1. Reconnect all of the disconnected modules.
  2. Install a scan tool.
  3. Turn ON the ignition, with the engine OFF.
  4. Wait for 10 seconds.

    The scan tool may require a power up reset before communication will occur due to a short on the high speed GMLAN serial data circuits. Turn OFF or disconnect the scan tool prior to performing this test.

  5. Select the Display DTCs function for each module.
  6. 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 14 
14  Did you record any DTCs which do not begin with a U? Go to Diagnostic Trouble Code (DTC) List - Vehicle Go to Step 15 
15 Did you diagnose all of the DTCs? Go to Step 16  Go to Step 13 
16 Use the scan tool in order to clear the DTCs.
Did you complete the action?		 System OK -
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