GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 Escalade 🢒 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 VCM (Gas) and PCM (Diesel) detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the VCM (Gas) and PCM (Diesel) 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, U1300 or U1305 will be set. Refer to DTC U1300 Class 2 Data Link Low or DTC U1300 Class 2 Data Link Low .
    • When the class 2 serial data circuit is shorted to B+ U1301 or U1305 will be set. Refer to DTC U1301 Class 2 Data Link High or DTC U1301 Class 2 Data Link High .

Step

Action

Value(s)

Yes

No

1
  1. Disconnect the scan tool from the data link connector (DLC).
  2. Turn the ignition switch to the RUN position.
  3. Connect a DMM between terminal 2 and 4 of the DLC.

Is the voltage reading greater than the specified value?

7 volts

Go to Step 2

Go to Step 9

2
  1. Turn the ignition to the OFF position.
  2. Disconnect connector C100.
  3. Connect a DMM between terminal 2 and 4 of the DLC.

Is the voltage reading greater than the specified value?

7 volts

Go to Step 5

Go to Step 3

3
  1. Turn the ignition to the OFF position.
  2. Reconnect connector  C100.
  3. Disconnect connector C1 of the electronic brake control module (EBCM).
  4. Connect a DMM between terminal 2 and 4 of the DLC.

Is the voltage reading greater than the specified value

7 volts

Go to Step 4

Go to Step 17

4
  1. Turn the ignition to the OFF position.
  2. Disconnect the vehicle control module (VCM) or powertrain control module (PCM).
  3. Connect a DMM between terminal 2 and 4 of the DLC.

Is the voltage reading greater than the specified value?

7 volts

Go to Step 7

Go to Step 17

5
  1. Turn the ignition to the OFF position.
  2. Disconnect the EVO/Passlock module (VTD).
  3. Connect a DMM between terminal 2 and 4 of the DLC.

Is the voltage reading greater than the specified value?

7 volts

Go to Step 6

Go to Step 17

6
  1. Turn the ignition to the OFF position.
  2. Disconnect the transfer case shift control module connector C1.
  3. Connect a DMM between terminal 2 and 4 of the DLC.

Is the voltage reading greater than the specified value

7 volts

Go to Step 8

Go to Step 17

7

Locate and repair the short to voltage in CKT 1807 (PPL) between C100 and the EBCM, VCM/PCM. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 18

--

8
  1. Locate and repair the short to voltage in CKT 1807  (PPL) between the DLC and the VTD, C100 and the transfer case shift control module. Refer to Wiring Repairs in Wiring Systems.
  2. Reconnect C100.

Is the repair complete?

--

Go to Step 18

--

9
  1. Turn the ignition switch to the OFF position.
  2. Connect a DMM (continuity) between cavity 2 of the DLC and ground.

Is continuity present?

--

Go to Step 10

Go to Step 18

10
  1. Disconnect connector C100.
  2. Connect a DMM (continuity) between cavity 2 of the DLC and ground.

Is continuity present?

--

Go to Step 13

Go to Step 11

11
  1. Reconnect connector C100.
  2. Disconnect connector C1 of the electronic brake control module (EBCM).
  3. Connect a DMM (continuity) between cavity 2 of the DLC and ground.

Is continuity present?

--

Go to Step 12

Go to Step 17

12
  1. Disconnect the vehicle control module (VCM) or powertrain control module (PCM).
  2. Connect a DMM (continuity) between cavity 2 of the DLC and ground.

Is continuity present?

--

Go to Step 15

Go to Step 17

13
  1. Disconnect the EVO/Passlock module (VTD).
  2. Connect a DMM (continuity) between cavity 2 of the DLC and ground.

Is the continuity present?

--

Go to Step 14

Go to Step 17

14
  1. Disconnect the transfer case shift control module connector C1.
  2. Connect a DMM (continuity) between cavity 2 of the DLC and ground.

Is continuity present?

--

Go to Step 16

Go to Step 17

15

Locate and repair the short to ground in CKT 1807 (PPL) between C100 and the EBCM, VCM/PCM. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 18

--

16
  1. Locate and repair the short to ground in CKT 1807  (PPL) between the DLC and the VTD, C100 and the transfer case shift control module. Refer to Wiring Repairs in Wiring Systems.
  2. Reconnect C100.

Is the repair complete?

--

Go to Step 18

--

17

Replace the control module that you disconnected last.

Is the repair complete?

--

Go to Step 18

--

18
  1. Use the scan tool to clear the DTCs
  2. Operate the vehicle within the conditions for running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 1

OK