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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 945 (DATA LINK COMMUNICATION SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESSCAN TOOL DOES NOT COMMUNICATE WITH HIGH SPEED GMLAN DEVICEDIAGNOSTIC AIDS
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Diagnostic Aids

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Aids
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
IMPORTANT: The scan tool communication with the modules connected only to high speed GMLAN data link requires the use of the CANdi module. Due to configuration of this vehicle, they may be communication DTCs set against modules that are able to communicate with the scan tool.

The following conditions may cause a total loss of high speed GMLAN data communication:

  • A short between high speed GMLAN (+) and high speed GMLAN (-) circuits
  • Any of the high speed GMLAN serial data circuits shorted to ground or voltage
  • A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits
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 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. Retrieve DTCs from the powertrain control module (PCM).
Did you record any DTCs in the range of U1881-U1899?		 Go to DTC U1881-U1899  Go to Step 3 
3 Did you record any DTCs in the range of U0100-U0299? Go to DTC U0100-U0299 (Diesel Engine) DTC U0100-U0299 (HP2)  Go to Step 4 
4 Attempt to communicate with the following modules:
  • The energy storage control module (ESCM)
  • The starter/generator control module (SGCM)
  • The electro-hydraulic power steering (EHPS) module

Does the scan tool communicate with all listed modules?		 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 high speed GMLAN (+) and (-) circuits
    • 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 12  Go to Diagnostic Aids
6
  1. Turn OFF the ignition.
  2. Disconnect the scan tool from the data link connector (DLC).
  3. 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 8  Go to Step 7 
7
  1. Disconnect the SGCM.
  2. Repair the high speed GMLAN serial data circuits between DLC connector and SGCM for an open. Refer to Wiring Repairs and Connector Repairs in Wiring Systems.
Did you complete the repair?		 Go to Step 8  -
8
  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  Go to Step 9 
9 Did you record any DTCs which do not begin with a "U"? Go to Step 10  Go to Step 11 
10 Diagnose the DTCs as directed by the diagnostic procedures for the particular module or concern.
Did you complete the action?		 Go to Step 11  -
11 Did you diagnose all of the DTCs? Go to Step 12  Go to Step 9 
12 Use the scan tool in order to clear the DTCs.
Did you complete the action?		 System OK -
RENDER: 1.0x

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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

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  • • The engine overheats, stalls repeatedly, or misfires under load.
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