GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 Envoy - 4WD 🢒 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.
  3. Inspect with known good male terminal from J-38125 repair kit.

Is the connection good?

--

Go to Step 4

Go to Step 6

4

Measure voltage from terminal 16 of the DLC to ground.

Does voltage equal the specified value?

B+

Go to Step 5

Go to Step 8

5

Measure the voltage from terminal 16 to terminal 4 of the DLC.

Is the voltage within the specified range?

B+

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 640 (ORN).

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

9

Repair an open in CKT 1850 (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 11

Go to Step 14

11

Is DTC U1000 or DTC U1xxx (lost communications with xxx) set in the modules that will communicate?

--

Go to Step 12

Go to Step 13

12

Use the CLASS 2 LOST COMMUNICATIONS WITH XXX (U1000) procedures, as appropriate, in order to diagnose the malfunction

Is the procedure complete?

--

Go to Diagnostic System Check - Data Link Communications

--

13

Use the CLASS 2 LOST COMMUNICATIONS WITH XXX (U1XXX) procedures in order to diagnose the malfunction for the module which is not communicating.

Is the procedure complete?

--

Go to Diagnostic System Check - Data Link Communications

--

14
  1. Turn the ignition switch to the OFF position.
  2. Inspect for proper connection of the scan tool to the DLC at terminal 5.
  3. Inspect with known good male terminal from repair kit J-38125.

Is the connection good?

--

Go to Step 15

Go to Step 6

15

Measure the resistance from terminal 16 to terminal 5 of the DLC.

Is the resistance within the specified range?

0-5 ohms

Go to Step 16

Go to Step 31

16
  1. Check for proper connection of the scan tool to the data link connector at terminal 2.
  2. Inspect with known good male terminal from repair kit J-38125.

Is the connection good?

--

Go to Step 17

Go to Step 6

17
  1. Disconnect splice pack SP201.
  2. Inspect for proper connection of the Class 2 serial data circuit to terminal A of the splice pack.

Is the connection good?

--

Go to Step 18

Go to Step 6

18

Measure the resistance from terminal 2 of the DLC to terminal A of the splice pack.

Is the resistance within the specified range?

0-5 ohms

Go to Step 19

Go to Step 30

19

Measure the resistance on the DLC from terminal 2 to terminal 4 with splice pack SP201 connected.

Is the resistance as specified?

OL (Infinite)

Go to Step 20

Go to Step 21

20
  1. Ensure that SP201 is connected.
  2. Using the J 35616-A , connect the positive lead of the J 39200 DMM to pin 2 of the DLC.
  3. Connect the negative lead of the J 39200 DMM to pin 4 of the DLC.
  4. Set the meter to measure DC voltage.
  5. Select the 40 V manual range.
  6. Press the MIN/MAX button.
  7. Press the PEAK MIN/MAX button.

    8. The top of the meter display should read 1ms RECORD MAX.

  8. Turn the ignition switch to the RUN position.

Is the MAX voltage within the specified range?

5-8 V

Go to Step 21

Go to Step 27

21
  1. Turn the ignition switch to the OFF position.
  2. Use the correct terminal adapter from J 35616-A in order to connect a jumper wire to terminal A of the splice pack SP 201.
  3. Connect the other end of the jumper wire (with the correct terminal adapter) to a terminal in the splice pack SP 201 that is connected to a module.
  4. Turn the ignition switch to the RUN position.
  5. Use the scan tool in order to attempt to establish communication with the module that is jumpered to the DLC.

May communication be established?

--

Go to Step 22

Go to Step 23

22

Repeat step 20 for each module on the Class 2 serial data link.

May communication be established for each module on the Class 2 serial data link?

--

Go to Step 32

Go to Step 23

23
  1. Turn the ignition switch to the OFF position.
  2. Disconnect the module which does not communicate.
  3. Measure the resistance from the splice pack SP 201 terminal of the Class 2 serial data circuit for the disconnected module to ground.

Is the resistance as specified?

OL (Infinite)

Go to Step 24

Go to Step 29

24
  1. Turn the ignition switch to the RUN position.
  2. Measure the voltage from the Class 2 serial data circuit of the disconnected module to ground.

Is the voltage within the specified range?

0-1 V fluctuating

Go to Step 25

Go to Step 28

25
  1. Turn the ignition switch to the OFF position.
  2. Inspect the connector of the disconnected module in the area of the Class 2 serial data circuit for backed out terminals that may cause an open circuit or an intermittent connection.

Are all terminals properly locked in to the connector body?

--

Go to Step 26

Go to Step 6

26
  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 the splice pack SP 201.
  3. Reconnect all the modules on the Class 2 serial data link.
  4. Turn the ignition switch to the RUN position.
  5. Use the scan tool in order to attempt to establish communication with the module which was replaced.

May communications be established?

--

Go to Step 32

Go to Step 27

27

Replace the Class 2 serial data circuit wire between the splice pack SP 201 and the module that does not communicate.

Is the repair complete?

--

Go to Step 32

--

28
  1. Turn the ignition switch to the OFF position.
  2. Repair the short to voltage in the Class 2 serial data circuit.

Is the repair complete?

--

Go to Step 32

--

29

Repair the short to ground in the Class 2 serial data circuit.

Is the repair complete?

--

Go to Step 32

--

30

Repair the open in the Class 2 serial data circuit.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

31

Repair the open in CKT 451.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

32
  1. Reconnect the splice pack SP 201.
  2. Reconnect all the modules on the Class 2 serial data link.
  3. Turn the ignition switch to the RUN position.
  4. Wait for 10 seconds.
  5. Inspect for DTCs in each module on the Class 2 serial data link.

Do any DTCs exist that begin with a U set with a current status?

--

Go to Step 34

Go to Step 33

33

Are any DTCs set that do not begin with a U?

--

Go to Step 34

Go to Step 35

34

Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction.

Is the procedure complete?

--

Go to Step 35

--

35

Have all DTCs been diagnosed?

--

Go to Step 36

Go to Step 34

36

Clear all of the DTCs.

Is the repair complete?

--

System OK

--