Scan Tool Does Not Communicate with Class 2 Device. Chevrolet Blazer - 4WD

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2000 🢒 Blazer - 4WD - RHD 🢒 Body and Accessories 🢒 Data Link Communications 🢒 Scan Tool Does Not Communicate with Class 2 Device

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 DLC allows communication with the modules for diagnostic purposes. Diagnostic trouble codes (DTCs) may be set due to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory.

Diagnostic Aids

•	The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must be connected to the DLC for any other module to communicate with the scan tool.

•	When the class 2 serial data circuit is shorted to ground, DTC U1300 will be set. Refer to DTC U1300 Class 2 Data Link Low .

•	When the class 2 serial data circuit is shorted to B+, DTC U1301 will be set. Refer to DTC U1301 Class 2 Data Link High .

Test Description

The number(s) below refer to the step number(s) 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 the class 2 serial data circuit:

•	The body control module (BCM)

•	The driver information display module

•	The electronic brake control module (EBCM)

•	The electronic climate control module (ECCM)

•	The inflatable restraint sensing and diagnostic module (SDM)

•	The instrument cluster

•	The seat adjuster memory module, RH

•	The transfer case shift control module (TCCM)

•	The vehicle control module (VCM)

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 or U1255 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.

A poor connection at terminal A would cause this condition but will not set a DTC.

An open in the class 2 serial data circuit between the DLC and S201 will prevent the scan tool from communicating with a module. This condition will not set a DTC.

The class 2 serial data circuit is shorted to voltage or ground. The condition may be due to the wiring or due to a malfunction in one of the modules. When testing the wire for a short, ensure that a module is not connected to the wire being tested. This test isolates the BCM class 2 serial data circuit.

The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must remain connected to the DLC for any other module to communicate with the scan tool. This test isolates the VCM class 2 serial data circuit.

This test isolates the ECC class 2 serial data circuit.

This test isolates the TCCM class 2 serial data circuit.

This test isolates the EBCM class 2 serial data circuit.

This test isolates the SDM class 2 serial data circuit.

This test isolates the instrument cluster class 2 serial data circuit.

This test isolates the seat adjuster memory module class 2 serial data circuit.

This test isolates the driver information display module class 2 serial data circuit.

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

Value(s)

Yes

Does the scan tool power up?

Go to Step 2

Go to Scan Tool Does Not Power Up

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 7

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 Diagnostic Aids

Are the 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 in Wiring Systems:

•	Testing for Intermittent Conditions and Poor Connections

•	Circuit Testing

•	Connector Repairs

•	Wiring Repairs

Did you find and correct the condition?

Go to Step 31

Go to Step 6

Is U1000 or U1255 the only DTC displayed in the previously specified range?

Go to DTC U1000 and DTC U1255 Class 2 Communication Malfunction

Go to DTC U1001-U1254 Lost Communication with XXX

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 in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References for the applicable Diagnostic System Check

Go to Step 8

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

Did you find and correct the condition?

Go to Control Module References for the applicable Diagnostic System Check

Go to Step 9

Inspect for poor connections at S201. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References for the applicable Diagnostic System Check

Go to Step 10

Test the class 2 serial data circuit for an open or a short between the DLC terminal 2 and S201. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References for the applicable Diagnostic System Check

Go to Step 11

Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the BCM.

Does the scan tool communicate with the BCM?

Go to Step 13

Go to Step 12

Turn OFF the ignition.
Disconnect the BCM.
Test the class 2 serial data circuit between S201 and the BCM 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the VCM.

Does the scan tool communicate with the VCM?

Go to Step 15

Go to Step 14

Turn OFF the ignition.
Disconnect the VCM.
Test the class 2 serial data circuit between S201 and the VCM 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the ECC module.

Does the scan tool communicate with the ECC module?

Go to Step 17

Go to Step 16

Turn OFF the ignition.
Disconnect the auxiliary power connector.
Test the class 2 serial data circuit between S201 and the ECC 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the TCCM.

Does the scan tool communicate with the TCCM?

Go to Step 19

Go to Step 18

Turn OFF the ignition.
Disconnect the TCCM.
Test the class 2 serial data circuit between S201 and the TCCM 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

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 21

Go to Step 20

Turn OFF the ignition.
Disconnect the EBCM.
Test the class 2 serial data circuit between S201 and the EBCM 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the SDM.

Does the scan tool communicate with the SDM?

Go to Step 23

Go to Step 22

Turn OFF the ignition.
Disconnect SDM.
Test the class 2 serial data circuit between S201 and the SDM 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 in Wiring System.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the instrument cluster.

Does the scan tool communicate with the instrument cluster?

Go to Step 25

Go to Step 24

Turn OFF the ignition.
Disconnect the instrument cluster.
Test the class 2 serial data circuit between S201 and the instrument cluster 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the seat adjuster memory module, RH.

Does the scan tool communicate with the seat adjuster memory module, RH?

Go to Step 27

Go to Step 26

Turn OFF the ignition.
Disconnect the seat adjuster memory module, RH.
Test the class 2 serial data circuit between S201 and the seat adjuster memory 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

Turn ON the ignition leaving the engine OFF.
Attempt to communicate with the driver information display module.

Does the scan tool communicate with the driver information display module?

Go to Step 31

Go to Step 28

Turn OFF the ignition.
Disconnect the driver information display module.
Test the class 2 serial data circuit between S208 and the driver information display 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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

Inspect for poor connections at the class 2 serial data circuit of the module that is not communicating. 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 31

Go to Step 30

Replace the module which is not communicating. Refer to Control Module References for the appropriate repair instructions.

Did you complete the replacement?

Go to Step 31

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 or disconnect 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 Step 33

Go to Step 32

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

Go to Step 33

Go to Step 35

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

Did you complete the action?

Go to Step 34

Did you diagnose all of the DTCs?

Go to Step 35

Go to Step 33

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK