Scan Tool Does Not Communicate with Class 2 Device. Cadillac CTS 2007

For 1990-2009 cars only

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Scan Tool Does Not Communicate with Class 2 Device LHD

Circuit Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the data link connector (DLC) allows communication with the modules for diagnostic purposes.

Diagnostic Aids

The engine will not start when there is a total loss of class 2 serial data communication while the ignition is OFF. The following conditions will cause a total loss of class 2 serial data communication:

•	A class 2 serial data circuit shorted to ground.

•	A class 2 serial data circuit shorted to voltage.

•	An internal condition within a module or connector on the class 2 serial data circuit, that causes a short to voltage or ground to the class 2 serial data circuit.

Test Description

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

A partial malfunction in the class 2 serial data circuit uses a different procedure from a total malfunction of the class 2 serial data circuit. The following modules communicate on class 2 serial data bus:

•	The audio amplifier (AMP)

•	The dash integration module (DIM)

•	The digital radio receiver (DRR)

•	The driver door module (DDM)

•	The driver door switch assembly (DDSA)

•	The electronic brake control module (EBCM)

•	The engine control module (ECM) for LY7/LP1 models communicates on both class 2 and high speed GMLAN links and communicate with the scan tool on high speed GMLAN

•	The front passenger door module (FPDM)

•	The HVAC control module

•	The inflatable restraint sensing and diagnostic module (SDM)

•	The instrument panel cluster (IPC)

•	The left rear door module (LRDM)

•	The memory seat module (MSM) w/A45

•

The radio

•	The radio antenna module

•	The rear integration module (RIM)

•	The right rear door module (RRDM)

•	The theft deterrent control module (VTD)

•	The TV antenna module

•	The vehicle communication interface module (VCIM)

The following DTCs may be retrieved with a history status, but are not the cause of the present condition.

A state of health DTC with a history status may be present along with a U1000 code having a current status. This indicates that the malfunction occurred when the ignition was ON.

Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.

This step takes out from the class 2 bus the modules connected to splice pack SP303, excepting SDM and RIM.

This step takes out from the class 2 bus the modules connected to splice pack SP300, excepting IPC.

This test isolates the class 2 serial data circuit between DLC and DIM.

This test localizes the class 2 serial data circuit of the suspected bus, that is shorted.

If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.

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

Step

Action

Yes

Schematic Reference: Data Communication Schematics

Connector End View Reference: Master Electrical Component List

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

Turn ON the ignition leaving the engine OFF.
Attempt to communicate with each module on the class 2 serial data circuit. If using a Tech 2, obtain this information using the class 2 Message Monitor feature.

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 3

Go to Step 8

Select the Display DTCs function for each module. If using a Tech 2, use the class 2 DTC Check feature in order to determine which modules do have DTCs set.
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 U1000 to U1305?

Go to Step 4

Go to Step 7

Are the history DTCs U1300, U1301 or U1305 retrieved from any module?

Go to Step 5

Go to Step 6

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 class 2 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following procedures:

•	Testing for Intermittent Conditions and Poor Connections

•	Circuit Testing

•	Connector Repairs

•	Wiring Repairs

Did you find and correct the condition?

Go to Step 22

Go to Step 6

Is U1000 the only DTC displayed in the previously specified range?

Go to DTC U1000

Go to DTC U1001-U1254

Diagnose the non-communicating module by using the DTC U1001-U1254 procedure for the module which is not communicating. Refer to DTC U1001-U1254 .

Did you complete the action?

Go to Diagnostic System Check - Vehicle

Turn OFF the ignition.
Disconnect the scan tool from the data link connector (DLC).
Inspect for poor connections at the DLC terminals 2 and 5. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Diagnostic System Check - Vehicle

Go to Step 9

Test the DLC ground circuit at terminal 5 for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Diagnostic System Check - Vehicle

Go to Step 10

Disconnect the splice pack SP303.
Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the dash integration module (DIM).

Does the scan tool communicate with the DIM?

Go to Step 18

Go to Step 11

Turn OFF the ignition.
Disconnect the splice pack SP300.
Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the DIM.

Does the scan tool communicate with the DIM?

Go to Step 18

Go to Step 12

Turn OFF the ignition.
Disconnect the splice pack SP200.
Test the class 2 serial data circuit between the splice pack SP200 and the DLC for an open, a short to ground, or a short to voltage. Turn ON the ignition leaving the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 22

Go to Step 13

Using the correct terminal adapter, connect a jumper wire to the DLC terminal of the splice pack SP200.
Connect the other end of the jumper wire, using correct terminal adapter, to the electronic brake control module (EBCM) terminal of the splice pack SP200.
Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the DIM.

Does the scan tool communicate with the DIM?

Go to Step 18

Go to Step 14

Turn OFF the ignition.
Disconnect the farthest module from the DLC that is still connected to class 2 serial data circuits.
Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the EBCM.

Does the scan tool communicate with the EBCM?

Go to Step 15

Go to Step 16

Turn OFF the ignition.
Test the class 2 serial data circuits of the disconnected module for an open, a short to ground or a short to voltage. Turn ON the ignition leaving the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 22

Go to Step 20

Is the EBCM the last module connected to class 2 data bus?

Go to Step 17

Go to Step 14

Disconnect the EBCM.
Test the class 2 serial data circuits of the disconnected module for an open, a short to ground or a short to voltage. Turn ON the ignition leaving the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 22

Go to Step 20

Using the appropriate jumper at the suspected splice pack, perform the following in order to determine which class 2 serial data circuit or module is causing the concern:

Turn ON the ignition, with the engine OFF.
Connect each previously disconnected module to the class 2 serial data circuit one at a time until communication with the class 2 serial data circuit is lost.

Did you complete the action?

Go to Step 19

Test the class 2 serial data circuits of the suspected module for a short to ground or a short to voltage. Turn ON the ignition leaving the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 22

Go to Step 20

Inspect for poor connections at the class 2 serial data circuit of the last disconnected module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 22

Go to Step 21

Replace the last disconnected module. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 22

Reconnect all of the disconnected modules.
Reconnect any other disconnected connectors.
Install a scan tool.
Turn ON the ignition leaving the engine OFF.
Wait for 10 seconds.

The scan tool may require a power up reset before communication will occur due to a short on the class 2 serial data circuit. Turn OFF the scan tool prior to performing this test.

Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.
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 - Vehicle

Go to Step 23

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

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 24

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

Scan Tool Does Not Communicate with Class 2 Device RHD

Circuit Description

Diagnostic Aids

•	A class 2 serial data circuit shorted to ground.

•	A class 2 serial data circuit shorted to voltage.

•	An internal condition within a module or connector on the class 2 serial data circuit, that causes a short to voltage or ground to the class 2 serial data circuit.

Test Description

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

•	The audio amplifier (AMP)

•	The dash integration module (DIM)

•	The digital radio receiver (DRR)

•	The driver door module (DDM)

•	The driver door switch assembly (DDSA)

•	The electronic brake control module (EBCM)

•	The engine control module (ECM)

•	The front passenger door module (FPDM)

•	The HVAC control module

•	The inflatable restraint sensing and diagnostic module (SDM)

•	The instrument panel cluster (IPC)

•	The left rear door module (LRDM)

•	The memory seat module (MSM) w/A45

•

The radio

•	The radio antenna module

•	The rear integration module (RIM)

•	The right rear door module (RRDM)

•	The theft deterrent control module (VTD)

•	The TV antenna module

•	The vehicle communication interface module (VCIM)

The following DTCs may be retrieved with a history status, but are not the cause of the present condition.

A state of health DTC with a history status may be present along with a U1000 code having a current status. This indicates that the malfunction occurred when the ignition was ON.

Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.

This step takes out from the class 2 bus the modules connected to splice pack SP300, except the SDM and the DIM.

This step takes out from the class 2 bus the modules connected to splice pack SP303, except the RIM.

This test isolates the class 2 serial data circuit between DLC and DIM.

This test localizes the class 2 serial data circuit of the suspected bus, that is shorted.

If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.

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

Step

Action

Yes

Schematic Reference: Data Communication Schematics

Connector End View Reference: Master Electrical Component List

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

Turn ON the ignition leaving the engine OFF.
Attempt to communicate with each module on the class 2 serial data circuit. If using a Tech 2, obtain this information using the class 2 Message Monitor feature.

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 3

Go to Step 8

Select the Display DTCs function for each module. If using a Tech 2, use the class 2 DTC Check feature in order to determine which modules do have DTCs set.
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 U1000 to U1305?

Go to Step 4

Go to Step 7

Are the history DTCs U1300, U1301 or U1305 retrieved from any module?

Go to Step 5

Go to Step 6

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 class 2 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following procedures:

•	Testing for Intermittent Conditions and Poor Connections

•	Circuit Testing

•	Connector Repairs

•	Wiring Repairs

Did you find and correct the condition?

Go to Step 22

Go to Step 6

Is U1000 the only DTC displayed in the previously specified range?

Go to DTC U1000

Go to DTC U1001-U1254

Diagnose the non-communicating module by using the DTC U1001-U1254 procedure for the module which is not communicating. Refer to DTC U1001-U1254 .

Did you complete the action?

Go to Diagnostic System Check - Vehicle

Turn OFF the ignition.
Disconnect the scan tool from the data link connector (DLC).
Inspect for poor connections at the DLC terminals 2 and 5. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Diagnostic System Check - Vehicle

Go to Step 9

Test the DLC ground circuit at terminal 5 for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Diagnostic System Check - Vehicle

Go to Step 10

Disconnect the splice pack SP300.
Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the dash integration module (DIM).

Does the scan tool communicate with the DIM?

Go to Step 18

Go to Step 11

Turn OFF the ignition.
Disconnect the splice pack SP303.
Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the DIM.

Does the scan tool communicate with the DIM?

Go to Step 18

Go to Step 12

Turn OFF the ignition.
Disconnect the splice pack SP201.
Test the class 2 serial data circuit between the splice pack SP201 and the DLC for an open, a short to ground, or a short to voltage. Turn ON the ignition leaving the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 22

Go to Step 13

Using the correct terminal adapter, connect a jumper wire to the DLC terminal of the splice pack SP201.
Connect the other end of the jumper wire, using correct terminal adapter, to the electronic brake control module (EBCM) terminal of the splice pack SP201.
Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the DIM.

Does the scan tool communicate with the DIM?

Go to Step 18

Go to Step 14

Turn OFF the ignition.
Disconnect the farthest module from the DLC that is still connected to class 2 serial data circuits.
Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the EBCM.

Does the scan tool communicate with the EBCM?

Go to Step 15

Go to Step 16

Turn OFF the ignition.
Test the class 2 serial data circuits of the disconnected module for an open, a short to ground or a short to voltage. Turn ON the ignition leaving the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 22

Go to Step 20

Is the EBCM the last module connected to class 2 data bus?

Go to Step 17

Go to Step 14

Disconnect the EBCM.
Test the class 2 serial data circuits of the disconnected module for an open, a short to ground or a short to voltage. Turn ON the ignition leaving the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 22

Go to Step 20

Using the appropriate jumper at the suspect splice pack, perform the following in order to determine which class 2 serial data circuit or module is causing the concern:

Turn ON the ignition, with the engine OFF.
Connect each previously disconnected module to the class 2 serial data circuit one at a time until communication with the class 2 serial data circuit is lost.

Did you complete the action?

Go to Step 19

Did you find and correct the condition?

Go to Step 22

Go to Step 20

Inspect for poor connections at the class 2 serial data circuit of the last disconnected module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 22

Go to Step 21

Replace the last disconnected module. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 22

Reconnect all of the disconnected modules.
Reconnect any other disconnected connectors.
Install a scan tool.
Turn ON the ignition leaving the engine OFF.
Wait for 10 seconds.

The scan tool may require a power up reset before communication will occur due to a short on the class 2 serial data circuit. Turn OFF the scan tool prior to performing this test.

Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.
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 - Vehicle

Go to Step 23

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

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 24

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK