LEMON Manuals: Even more car manuals for everyone
Home >> GMC >> 2004 >> Envoy RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 15 (Computer/Integrating Systems) >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with High Speed GMLAN Device >> Test Description

Test Description

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2005 Isuzu Ascender, 2005 GMC Envoy XUV, 2005 GMC Envoy XL, 2005 GMC Envoy, and 2005 Chevrolet TrailBlazer. 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 are connected to the high speed GMLAN serial data circuits:
    • ECM, for 5.3L
    • Transmission control module (TCM)
  2. 5:  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. 12:  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 (DLC) Schematics 
Connector End View Reference: Master Electrical Component List in Wiring Systems
1 Did you perform the Diagnostic System Check - Vehicle? Go to Step 2  Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
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 data bus.
Does the scan tool communicate with any module on the GMLAN serial data circuits?		 Go to Step 3  Go to Step 5 
3 Did you record any DTCs in the range of U2105 to U2199? Go to DTC U2105-U2199  Go to Step 4 
4
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 - Refer to Diagnostic Aids.
    • An intermittent open on any of the circuits
Refer to the following in Wiring Systems:Did you find and correct the condition?		 Go to Step 13  Go to Diagnostic Aids
5 
  1. Turn OFF the ignition.
  2. Inspect for poor connections at the DLC terminals 6 and 14. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 11  Go to Step 6 
6
  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 7  Go to Step 9 
7 Inspect for poor connections at the high speed GMLAN serial data circuits of the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 11  Go to Step 8 
8 Replace the ECM. Refer to Control Module References  for replacement, setup, and programming.
Did you complete the replacement?		 Go to Step 11  -
9
  1. Turn OFF the ignition.
  2. Disconnect the TCM.
  3. Test the high speed GMLAN circuits between the DLC and the TCM and between the TCM and the ECM for the following conditions:
    • An open
    • A short to ground
    • A short to battery
    • A short between them
Refer to the following in Wiring Systems:Did you find and correct the condition?		 Go to Step 11  Go to Step 10 
10 Replace the TCM. Refer to Control Module References  for replacement, setup, and programming.
Did you complete the replacement?		 Go to Step 11  -
11
  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 in Vehicle DTC Information Go to Step 12 
12  Did you record any DTCs which do not begin with a "U"? Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information Go to Step 13 
13 Use the scan tool in order to clear the history DTCs.
Did you complete the action?		 System OK -
scientia non olet · About LEMON Manuals