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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 XLR 🢒 Vehicle Control Systems 🢒 Computer/Integrating Systems 🢒 DTC U2105-U2199

Circuit Description

Important: For DTC U2153 refer to DTC U2153 in Navigation Systems.

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC U2105 Lost Communication With Engine Control Module (ECM)
    • DTC U2106 Lost Communication With Transmission Control Module (TCM)
    • DTC U2107 Lost Communication With Body Control Module (BCM)
    • DTC U2108 Lost Communication With Electronic Brake Control Module (EBCM)
    • DTC U2112 Lost Communication With Electronic Suspension Control (ESC) Module
    • DTC U2144 Lost Communication With Distance Sensing and Cruise Control (DSCC) Module

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms refer to DTC Symptom Description in Vehicle DTC Information.

Symptom

Symptom Descriptor

00

No additional information

Conditions for Running the DTCs
    • Voltage supplied to the modules is in the normal operating voltage range.
    • The vehicle power mode requires serial data communication to occur.
    • The DTC U2100 does not have a current status.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Action Taken When the DTC Sets

The module uses a default value for the missing parameter.

Conditions for Clearing the DTC
    • A current DTC clears when the malfunction is no longer present.
    • A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids
    • A poor connection at the inoperative module may cause this code to set.
    • An improperly powered module may cause this code to set.

Test Description

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

  1. If BCM detects an open in its class 2 circuit, the RCDLR takes control of the Run/Crank relay.

    2.

  2. A power moding code needs to be diagnosed first.

    3.

  3. The scan tool communicate with VCIM via class 2, so for high speed GMLAN data link diagnostic the VCIM will not be considered.

    4.

  4. The module which was not communicating due to an open in the high speed GMLAN serial data circuits may have set Loss of Communication DTCs for those modules that it was monitoring.

    5.

  5. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.

Step

Action

Yes

No

Schematic Reference: Data Link Connector 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

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With the scan tool check the Run/Crank Relay Command parameter from body control module (BCM) Data Display under Computer/Integrating System menu.

Does the scan tool display OFF?

Go to Step 3

Go to Step 5

3

Retrieve DTCs from RCDLR module.

Is the DTC B1440 set?

Go to DTC B1440

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the BCM.
  3. Test the class 2 serial data circuit of the BCM for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 15

5

Attempt to communicate with ESC module.

Were you able to communicate with ESC module?

Go to Step 10

Go to Step 6

6
  1. Turn OFF the ignition.
  2. Disconnect the vehicle communication interface module (VCIM).
  3. Bypass the VCIM installing jumpers between GMLAN serial data circuits at the VCIM connector:
    4. • Connect a jumper between high speed GMLAN bus (+) circuit to BCM and high speed GMLAN bus (+) circuit to the ESC module.
    • Connect a jumper between high speed GMLAN bus (-) circuit to BCM and high speed GMLAN bus (-) circuit to the ESC module.
  4. Attempt to communicate with ESC module.

Were you able to communicate with ESC module?

Go to Step 7

Go to Step 9

7

Test the high speed GMLAN serial data circuits of the VCIM for poor connections. 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 19

Go to Step 8

8

Important: Perform the module setup procedure if required.

Replace the VCIM. Refer to Control Module References .

Did you complete the replacement?

Go to Step 19

--

9
  1. Turn OFF the ignition.
  2. Test all the high speed GMLAN serial data circuits between BCM and ESC module for an open. Refer to the following:
    3. •  Control Module References for the applicable schematic
    •  Circuit Testing in Wiring Systems
    •  GMLAN Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 19

Go to Step 10

10

Important:: Use the DTC list from the DTC Descriptors to determine the closest module to DLC which is not communicating.

Test the following circuits of the module that is not communicating, for an open or a short to ground:

    • The battery positive circuits
    • The battery voltage output circuits
    • The switched battery positive voltage circuits

Refer to the following:

    •  Control Module References for the applicable schematic
    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 19

Go to Step 11

11
  1. Turn OFF the ignition.
  2. Test the ground circuits of the module that is not communicating, for an open. Refer to the following:
    3. •  Control Module References for the applicable schematic
    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 19

Go to Step 12

12

Test the high speed GMLAN serial data circuits of the module that is not communicating, for an open. Refer to the following:

    •  Control Module References for the applicable schematic
    •  Circuit Testing in Wiring Systems
    •  GMLAN Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 17

Go to Step 13

13

Test the following circuits of the module that is not communicating, for poor connections:

    • The battery positive voltage circuits
    • The battery voltage output circuits
    • The switched battery positive voltage circuits
    • The ground circuits
    • The high speed GMLAN serial data circuits

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 19

Go to Step 14

14

Important: Perform the module setup procedure if required.

Replace the module that is not communicating. Refer to Control Module References .

Did you complete the replacement?

Go to Step 19

--

15

Inspect for poor connections at the harness connector of the BCM. 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 19

Go to Step 16

16

Important: Perform the module setup procedure.

Replace the BCM. Refer to Body Control Module Replacement .

Did you complete the replacement?

Go to Step 19

--

17

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Retrieve DTCs from the module that was not communicating.

Does the scan tool display any DTCs which do not begin with a "U"?

Go to the Diagnostic System Check - Vehicle in Vehicle DTC Information

Go to Step 18

18

Use the scan tool in order to clear the DTCs.

Did you complete the action?

Go to Step 19

--

19

Retrieve DTCs from 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 the Diagnostic System Check - Vehicle in Vehicle DTC Information

Go to Step 20

20
  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?

System OK

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