GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Astro - 2WD 🢒 Body and Accessories 🢒 Data Link Communications 🢒 Scan Tool Does Not Communicate with Class 2 Data Line

Step

Action

Value(s)

Yes

No

1

Was the DLC System Check performed?

--

Go to Step  2

Go to Diagnostic System Check - Data Link Communications

2

May the scan tool be powered up?

--

Go to Step  10

Go to Step  3

3
  1. Disconnect the scan tool from the data link connector.
  2. Inspect for proper connection of the scan tool to the data link at terminal 4 and terminal 16.

Inspect with known good male terminal from J-38125 repair kit.

Is the connection good?

--

Go to Step  4

Go to Step  6

4

Using a DMM J 39200 ,measure voltage from terminal 16 of the DLC to ground.

Is the voltage within the specified value?

9.0 to 16.0 v

Go to Step  5

Go to Step  8

5

Using a DMM J 39200 ,measure the resistance from terminal 4 of the DLC to ground.

Is the resistance within the specified value?

0-5 ohms

Go to Step  7

Go to Step  9

6

Repair the connection as needed.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

Go to Step 3

7

Inspect the scan tool for a malfunction. Refer to the Scan Tool instruction manual.

Has a properly operating scan tool been obtained?

--

Go to Step 2

--

8

Repair an open in CKT 840 (ORN).

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

9

Repair open in CKT 750 (BLK).

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

10
  1. Turn the ignition switch to the RUN position.
  2. Use the scan tool in order to attempt to establish communication with each module on the Class 2 data link.

    3. If you use a Tech 2, use the Diagnostic Circuit Check Class 2 Message Monitor CLASS 2 MESSAGE MONITOR feature in order to obtain this information.

Are any of the modules on the Class 2 data link communicating?

--

Go to Step 19

Go to Step 11

11
  1. Turn the ignition switch to the OFF position.
  2. Inspect for proper connection of the scan tool to the DLC at terminal 5.

Inspect with known good male terminal from repair kit J-38125.

Is the connection good?

--

Go to Step  12

Go to Step 6

12

Using a DMM J 39200 , measure the voltage from terminal 16 to terminal 5 of the DLC.

Is the voltage within the specified value?

9.0 to 16.0 v

Go to Step  13

Go to Step  28

13

Check for proper connection of the scan tool to the data link connector at terminal 2.

Inspect with known good male terminal from repair kit J-38125.

Is the connection good?

--

Go to Step  14

Go to Step 6

14
  1. Turn the ignition switch to the RUN position.
  2. Using a DMM J 39200 , measure the voltage on the DLC from terminal 2 to terminal 4.

Is the voltage within the specified value and fluctuating?

0 to 2.0 V

Go to Step  19

Go to Step  15

15

Is the voltage above the specified value and steady?

2.0 V

Go to Step  16

Go to Step  17

16

Repair the short to Voltage in the Class 2 circuit.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

17
  1. Turn the ignition switch to the OFF position.
  2. Using a DMM J 39200 , measure the resistance from terminal 2 of the DLC to ground.

Is the resistance within the specified value?

OL (Infinite)

Go to Step  19

Go to Step  18

18

Repair the short to ground in the Class 2 circuit.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

19
  1. Disconnect the module that does not communicate.
  2. Turn the ignition switch to the RUN position.
  3. Using a DMM J 39200 , measure the voltage between circuit 1807 of the following affected module and ground:
    4. • VCM connector C4 cavity 11
    • EBCM connector C1 cavity G
    • Passlock Module cavity B4
    • ATC Shift Module connector C1 cavity E9
    • Overhead Console connector C1 cavity H

Is the voltage within the specified value and fluctuating?

0 to 2.0 V

Go to Step 21

Go to Step  20

20

Repair the open in circuit 1807 between the module and the DLC.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

21

Using a DMM J 39200 , measure the resistance between the ground terminal(s) at the following affected module and ground:

    • VCM connector C3 cavity 17, connector C3 cavity 18
    • EBCM connector C1 cavity J, connector C3 cavity B
    • Passlock Module cavity B1
    • ATC Shift Module connector C1 cavity E15, connector C1 cavity 16, connector C2 cavity C
    • Overhead Console connector C1 cavity F

Is the resistance within the specified value?

0 to 5.0 ohms

Go to Step  23

Go to Step  22

22

Repair the open in the ground circuit to the specified module.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

23

Using a DMM J 39200 , measure the voltage between the B+ terminal(s) at the following affected module and ground.

    • VCM connector C3 cavity 21
    • EBCM connector C3 cavity A
    • Passlock Module cavity B8
    • ATC Shift Module connector C2 cavity D
    • Overhead Console functions do not get a B+ supply.

Is the voltage within the specified value?

9.0 to 16.0 v

Go to Step  25

Go to Step  24

24

Repair the open in the B+ circuit to the specified module.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

25

Using a DMM J 39200 , measure the voltage between the ignition terminal(s) at the following affected module and ground.

    • VCM connector C4 cavities 13, 18
    • EBCM connector C1 cavity A
    • Passlock Module cavity B3
    • ATC Shift Module connector C1 cavity E10
    • Overhead Console connector C1 cavity E

Is the voltage within the specified value?

9.0 to 16.0 v

Go to Step  27

Go to Step  26

26

Repair the open in the ignition circuit to the specified module.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

27
  1. Replace the module that does not communicate.

    2. Refer to the appropriate on-vehicle service procedures for the module being replaced in order to ensure a complete repair.

  2. Reconnect all the disconnected modules and components on the Class 2 serial data link.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

28

Repair the open in CKT 550/551/651 between DLC terminal 5 and Ground G105/G107.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--