GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2006 🢒 ION 🢒 Vehicle Control Systems 🢒 Computer/Integrating Systems 🢒 Scan Tool Does Not Communicate with Low Speed GMLAN Device

Modules connected to the GMLAN serial data circuit monitor for serial data communications on the GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module detects a bus-off condition a DTC U2100 will be set. This DTC can be retrieved as history only.

Diagnostic Aids

The engine will not start when there is a total malfunction of the GMLAN serial data circuits while the engine is not running. The following conditions may cause a total loss of GMLAN data communication:

    • Any of the serial data circuits shorted to ground
    • Any of the serial data circuits shorted to voltage
    • A short between serial data circuits
    • An internal malfunction of a module on the GMLAN network that causes a short to voltage or ground

Step

Action

Yes

No

Schematic Reference: Data Link Connector 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 the ignition ON, with the engine OFF.
  2. Attempt to communicate with each module on the GMLAN serial data circuit using a scan tool with an inline CANdi adaptor module properly installed.

Does the scan tool communicate with all modules on the GMLAN serial data circuits?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3
  1. Disconnect the scan tool from the data link connector (DLC).
  2. Turn the ignition OFF.
  3. Disconnect all non-communicating modules on the low speed GMLAN serial data circuit.
  4. Turn the ignition ON, with the engine OFF.
  5. Test the low speed GMLAN serial data circuit between the DLC and all the modules on the low speed GMLAN serial data circuit, for the following conditions:
    6. • An open
    • A short to ground
    • A short to voltage

Refer to the following:

    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 4

4

Test the following circuits of the module that is not communicating for an open or high resistance:

    • The battery positive voltage input circuits
    • The battery voltage output circuits
    • The ignition voltage input circuits
    • The ignition voltage output circuits
    • The switched battery positive voltage supply circuits
    • The ground circuits

Refer to the following:

    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 5

5

Inspect for poor connections and terminal tension at the following harness connector circuits of the module that is not communicating:

    • 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 low speed GMLAN serial data circuits

Refer to the following:

    •  Connector Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6

Replace the module that is not communicating on the low speed GMLAN serial data circuit. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 7

--

7
  1. Connect all modules and connectors.
  2. Connect the scan tool to the DLC.
  3. Turn the ignition ON, with the engine OFF.
  4. Perform the Diagnostic System Check for the system exhibiting symptoms. Refer to Control Module References .

Did you complete the operation?

System OK

Go to Step 2