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Test Description

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.

The number below refers to the step number on the diagnostic table.

  1. 12:  The module which was not communicating may have set Loss of Communication DTCs for those modules that it was monitoring.
DTC U0100-U0299 (HP2)

Step Action Yes No
Schematic Reference: Data Link Connector (DLC) Schematics 
Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views in Wiring Systems
1
  1. Turn ON the ignition, with the engine OFF.
  2. Install the scan tool with the CANdi module attached to it.
  3. Attempt to communicate with the following modules:
    • The energy storage control module (ESCM)
    • The starter/generator control module (SGCM)
    • The elctro-hydraulic power steering (EHPS) module
Does the scan tool communicate with any of the listed modules?		 Go to Step 7  Go to Step 2 
2
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 high speed GMLAN serial data circuits at the data link connector (DLC) for the following conditions:
  • A short to ground
  • A short to voltage
  • A short between high speed GMLAN (+) and GMLAN (-) circuits
Refer to the following in Wiring Systems:Did you find any of the above conditions?		 Go to Step 3  Go to Step 7 
3 Repeat the following steps on high speed GMLAN serial data circuits until the short found in the previous step at the DLC connector disappears, or until all modules are disconnected.
  1. Disconnect the high speed GMLAN modules, one at a time, in the following order:
    1. The powertrain control module (PCM)
    2. The hybrid control module (HCM)
    3. The EHPS
    4. The SGCM
    5. The ESCM
  2. Test the high speed GMLAN serial data circuits at the DLC connector for the short found at step 2.

Does the short found at step 2 at the DLC sill exist?		 Go to Step 6  Go to Step 4 
4
IMPORTANT: If only the PCM was disconnected on step 3, answer No at this step.
Test the high speed GMLAN serial data circuits between the last 2 disconnected modules for the short found at step 2.Did you find and correct the condition?		 Go to Step 12  Go to Step 5 
5 Consider the last disconnected module as the non communicating module for the following steps. Go to Step 10  -
6 Repair the high speed GMLAN serial data circuits between the DLC and the ESCM/SGCM for the short found in step 2.
Refer to the following in Wiring Systems:
Did you complete the repair?		 Go to Step 12  -
7
IMPORTANT: Use the DTC Descriptors list in order to determine which module is not communicating. If multiple DTCs were set, consider the closest module to the PCM as the non-communicating module.
Test the following circuits of the module that is not communicating for an open or a short to ground:
  • 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 circuits
Refer to the following procedures:Did you find and correct the condition?		 Go to Step 12  Go to Step 8 
8
  1. Turn OFF the ignition.
  2. Test the ground circuits of the module that is not communicating for an open.
Refer to the following procedures:Did you find and correct the condition?		 Go to Step 12  Go to Step 9 
9 Test the high speed GMLAN serial data circuits of the module that is not communicating for an open. Refer to Circuit Testing andWiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 12  Go to Step 10 
10 Inspect the harness connectors of the module that is not communicating for poor connections and terminal tension at the following circuits:
  • 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
  • The high speed GMLAN serial data circuits

Refer to the following procedures:
Did you find and correct the condition?		 Go to Step 12  Go to Step 11 
11
IMPORTANT: Perform the programming or set up procedure for the module, if required.
Replace the module that is not communicating. Refer to Control Module References in Body Control System for the applicable replacement procedure.Did you complete the replacement?		 Go to Step 12  -
12 
  1. Reconnect all disconnected components, if applicable.
  2. Install a scan tool.
  3. Turn ON the ignition, with the engine OFF.
  4. Select the Display DTCs function for the module which was not communicating.
Does the scan tool display any DTCs which do not begin with a "U"?		 Go to Control Module References for the applicable Diagnostic System Check Go to Step 13 
13 Select the Display DTCs function for the modules which had the Loss of Communications DTC set.
Does the scan tool display any DTCs which do not begin with a "U"?		 Go to Control Module References for the applicable Diagnostic System Check Go to Step 14 
14
  1. Use the scan tool in order to clear the DTCs.
  2. Continue diagnosing or clearing the DTCs until all the modules have been diagnosed and all the DTCs have been cleared.
Did you complete the action?		 Go to Control Module References for the applicable Diagnostic System Check -
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