Scan Tool Does Not Communicate with Class 2 Device. GMC Truck Savana 2000

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2000 🢒 Savana 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 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

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

•	When the class 2 serial data circuit is shorted to B+ 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:

•

EBCM

•	Passlock™ Module (Domestic)

•	PCM (Diesel)

•

VCM (Gas)

•	VIM (Export)

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.

This tests for a poor ground circuit or connection.

An open in the class 2 serial data circuit between the DLC and splice S207 will prevent the scan tool from communicating with any module. This condition will not set a DTC.

This test isolates the class 2 serial data circuit. When attempting to isolate a particular module, it is necessary to disconnect the other module due to the redundant connection between the two.

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 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 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 19

Go to Step 6

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

Go to Step 7

Go to DTC U1001-U1254 Lost Communication with XXX

Diagnose the malfunction using DTC U1001-U1254 Lost Communication with XXX .

Did you complete the action?

Go to Control Module References or the applicable Diagnostic System Check

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 or the applicable Diagnostic System Check

Go to Step 9

Test the DLC ground CKT 451 (BLK/WHT) CKT 551 (TAN/WHT) 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 or the applicable Diagnostic System Check

Go to Step 10

Disconnect the electronic brake control module (EBCM) connector C1.
Test the class 2 serial data CKT 1807 (PPL) for an open between the DLC terminal 2 and the EBCM connector C1 terminal G. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References or the applicable Diagnostic System Check

Go to Step 11

Leave the EBCM disconnected.
Turn ON the ignition leaving the engine OFF.
Attempt to establish communications with the vehicle control module (VCM - gas) or the powertrain control module (PCM - diesel).

Does the scan tool communicate with the VCM/PCM?

Go to Step 13

Go to Step 12

Turn OFF the ignition.
Disconnect the vehicle control module (VCM - gasoline engines) or the powertrain control module (PCM - diesel engines).
Turn ON the ignition leaving the engine OFF.
Attempt to establish communications with the Passlock™ module (domestic) or the vehicle immobilizer module (VIM - export).

Does the scan tool communicate with the Passlock™ module (domestic) or the vehicle immobilizer module (VIM - export)?

Go to Step 14

Go to Step 15

Inspect for poor connections at the EBCM. 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

Inspect for poor connections at the VCM/PCM. 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 17

Inspect for poor connections at the Passlock™ module or VIM. 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 18

Replace the EBCM. Refer to Control Module References for the appropriate repair instructions.

Did you complete the replacement?

Go to Step 19

Replace the VCM/PCM. Refer to Control Module References for the appropriate repair instructions.

Did you complete the replacement?

Go to Step 19

Replace the Passlock™ module or VIM. Refer to Control Module References .

Did you complete the replacement?

Go to Step 19

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 21

Go to Step 20

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

Go to Step 21

Go to Step 23

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 22

Did you diagnose all of the DTCs?

Go to Step 23

Go to Step 21

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK