GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2003 🢒 ION 🢒 HVAC 🢒 Heating, Ventilation and Air Conditioning 🢒 Scan Tool Does Not Communicate with CAN 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.

Test Description

The numbers below refer to the step numbers on the diagnostic table:

  1. A partial malfunction in the GMLAN serial data circuits uses a different procedure from a total malfunction of the GMLAN data circuits. The following modules communicate on the GMLAN serial data circuits:

    2. • Engine control module (ECM)
    • Transmission control module (TCM)

  2. The DTC U2100 may be retrieved with a history status, but is not the cause of the present condition.

    3.

  3. Data link connector terminals 6 and 14 provide the connection to the GMLAN serial data (+) circuit and the GMLAN serial data (-) circuit respectively.

    4.

  4. The communication malfunction may have prevented diagnosis of the customer complaint.

Step

Action

Yes

No

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 a CANdi adaptor in-line module properly installed.

Does the scan tool communicate with any module on the GMLAN serial data circuits?

Go to Step 3

Go to Step 5

3

  1. Select the Display DTCs function for each module.
  2. Record all of the displayed DTCs, the DTC status and the module which set the DTC.

Did you record any DTCs in the range of U2100 to U2172?

Go to Step 4

Go to Diagnostic Aids

4

Is the DTC U2100 retrieved from any module?

Go to Step 5

Go to DTC U2106

5

Important:: Turn the ignition ON, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions.

Test the GMLAN serial data circuits for an intermittent short to ground, an intermittent short to voltage or an intermittent short between GMLAN (+) and GMLAN (-). Refer to Data Link Connector Schematics and the following in Wiring Systems:

    •  Circuit Testing
    •  Connector Repairs
    •  Wiring Repairs

Did you find and correct the condition?

Go to Step 14

Go to Step 6

6

  1. Turn the ignition OFF.
  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 14

Go to Step 7

7
  1. Disconnect the TCM module from the GMLAN serial data circuits. Refer to Data Link Connector Schematics
  2. Turn the ignition ON, with the engine OFF.
  3. Attempt to communicate with the ECM.

Does the scan tool communicate with the ECM?

Go to Step 10

Go to Step 8

8
  1. Turn the ignition OFF.
  2. Disconnect the ECM from the GMLAN serial data circuits. Refer to Data Link Connector Schematics
  3. Reconnect the TCM to the GMLAN serial data circuit.
  4. With a jumper wire jump the High Speed GMLAN serial data (+) circuits on the ECM harness connector together.
  5. With a jumper wire jump the High Speed GMLAN serial data (-) circuits on the ECM harness connector together.
  6. Turn the ignition ON, with the engine OFF.
  7. Attempt to communicate with the TCM.

Does the scan tool communicate with the TCM?

Go to Step 11

Go to Step 9

9
  1. Enter the OFF mode.
  2. Make certain that both the ECM and the TCM are disconnected from the GMLAN serial data bus.
  3. Test the GMLAN serial data circuits between all modules and the DLC connector for:
    4. • Continuity
    • Short to ground
    • Short to battery
    • Short between them

Did you find and correct the condition?

Go to Step 14

Go to Step 13

10

Inspect for poor connections at the GMLAN serial data circuits of the TCM. 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 14

Go to Step 12

11

Inspect for poor connections at the 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 14

Go to Step 13

12

Important: Perform the module setup procedure if required.

Replace the TCM module. Refer to Control Module References in Body control System for the appropriate repair instructions.

Did you complete the replacement?

Go to Step 14

--

13

Important: Perform the module setup procedure if required.

Replace the ECM module. Refer to Control Module References in Body Control System for the appropriate repair instructions.

Did you complete the replacement?

Go to Step 14

--

14
  1. Connect all of the disconnected modules.
  2. Connect any other disconnected connectors.
  3. Install a scan tool.
  4. Turn the ignition ON, with the engine OFF.
  5. Wait for 10 seconds.

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

Does the Scan Tool communicate with the GMLAN serial data bus.

Go to Step 15

Go to Step 5

15
  1. Select the Display DTCs function for each module.
  2. 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 Step 17

Go to Step 16

16

Did you record any DTCs which do not begin with a "U"?

Go to Step 17

Go to Step 19

17

Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction. Refer to Control Module References in Body Control System for the applicable Diagnostic System Check.

Did you complete the action?

Go to Step 18

--

18

Did you diagnose all of the DTCs?

Go to Step 19

Go to Step 17

19

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

--