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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 Eldorado 🢒 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 Aids

The engine will not start when there is a total malfunction of the class 2 serial data circuit while the engine is not running.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. 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.

    2.

  2. The DTC U1300 and U1301 may be retrieved with a history status. These DTCs are not the cause of the present condition.

    3.

  3. A State of Health DTC with a history status may be present along with a U1000 or a U1255 with a current status. This indicates that the malfunction occurred when the ignition was on.

    4.

  4. The memory seat module (MSM), and the remote function actuator (RFA) are not monitored by other modules. When one of these modules is not communicating, diagnose the malfunction using the specified procedure.

    5.

  5. Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.

    6.

  6. An open in the class 2 serial data circuit between the DLC and splice S203 will prevent the scan tool from communicating with any module. This condition will not set a DTC.

    7.

  7. If there are no current DTCs that begin with a U, the communication malfunction has been repaired.

    8.

  8. The communication malfunction may have prevented diagnosis of the customer complaint.

Step

Action

Yes

No

1

Does the scan tool power up?

Go to Step 2

Go to Scan Tool Does Not Power Up

2
  1. Turn ON the ignition with the engine OFF.
  2. 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

3
  1. 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.)
  2. 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

4

Are the DTCs U1300, U1301 or U1305 retrieved from any module?

Go to Step 5

Go to Step 6

5

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:

    •  Circuit Testing
    •  Connector Repairs
    •  Wiring Repairs

Did you find and correct the condition?

Go to Step 54

Go to Step 6

6

Are U1000 or U1255 the only DTCs displayed in the previously specified range?

Go to DTC U1000 and DTC U1255 Class 2 Communication Malfunction

Go to DTC U1001-U1254 Loss of XXX Communications

7

Diagnose the malfunction using the DTC U1XXX Loss of XXX Communications procedures for the module which is not communicating. Refer to DTC U1001-U1254 Loss of XXX Communications .

Did you complete the action?

Go to Control Module References for the applicable Diagnostic System Check.

--

8
  1. Turn OFF the ignition.
  2. Disconnect the scan tool from the data link connector (DLC).
  3. Inspect for poor connections at terminals 2 and 5 of the DLC. 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 9

9

Test the ground circuit at terminal 5 of the DLC 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 10

10

Test the class 2 serial data circuit for an open or short to ground or voltage between the DLC and splice S203. 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

11
  1. Disconnect the powertrain control module (PCM).
  2. Turn ON the ignition with the engine OFF.
  3. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 12

Go to Step 13

12

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming in Engine Controls.

Did you complete the repair?

Go to Step 54

--

13
  1. Turn OFF the ignition.
  2. Disconnect the electronic brake control module (EBCM).
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 14

Go to Step 16

14

Test the class 2 serial data circuit between the EBCM and the PCM for a short to ground or voltage. (Turn ON the ignition with 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 54

Go to Step 15

15

Replace the EBCM. Refer to Electronic Brake Control Module Replacement in Antilock Brake System.

Did you complete the repair?

Go to Step 54

--

16
  1. Turn OFF the ignition.
  2. Disconnect the radio.
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 17

Go to Step 18

17

Replace the radio. Refer to Radio Replacement in Entertainment.

Did you complete the repair?

Go to Step 54

--

18
  1. Turn OFF the ignition.
  2. Disconnect the instrument cluster.
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 19

Go to Step 20

19

Replace the instrument cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges and Console.

Did you complete the repair?

Go to Step 54

--

20
  1. Turn OFF the ignition.
  2. Disconnect the climate control panel (CCP).
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 21

Go to Step 23

21

Test the class 2 serial data circuit between the instrument cluster and the CCP for a short to ground or voltage. (Turn ON the ignition with 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 54

Go to Step 22

22

Replace the CCP. Refer to Control Assembly Replacement in HVAC System--Automatic.

Did you complete the repair?

Go to Step 54

--

23

Is the vehicle equipped with A45?

Go to Step 24

Go to Step 27

24
  1. Turn OFF the ignition.
  2. Disconnect the memory mirror module (MMM).
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 25

Go to Step 27

25

Test the class 2 serial data circuit between the MMM and the CCP for a short to ground or voltage. (Turn ON the ignition with 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 54

Go to Step 26

26

Replace the MMM. Refer to Memory Mirror Module Replacement in Doors.

Did you complete the repair?

Go to Step 54

--

27
  1. Turn OFF the ignition.
  2. Disconnect the heater and A/C programmer (HCM).
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 28

Go to Step 30

28

Test the class 2 serial data circuit between the heater and A/C programmer (HCM) and the following component:

    • The MMM (w/A45)
    • The CCP (w/o A45)

for a short to ground or voltage. (Turn ON the ignition with 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 54

Go to Step 29

29

Replace the heater and A/C programmer (HCM). Refer to Programmer Replacement in HVAC System--Automatic.

Did you complete the repair?

Go to Step 54

--

30

Is the vehicle equipped with a cellular telephone module?

Go to Step 31

Go to Step 33

31
  1. Turn OFF the ignition.
  2. Disconnect the cellular telephone module.
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 32

Go to Step 33

32

Replace the cellular telephone module. Refer to Radio Frequency Booster and Bracket Assembly Replacement in Cellular Communication.

Did you complete the repair?

Go to Step 54

--

33

Is the vehicle equipped with A45?

Go to Step 34

Go to Step 37

34
  1. Turn OFF the ignition.
  2. Disconnect the memory seat module (MSM).
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 35

Go to Step 37

35

Test the class 2 serial data circuit between the MSM and the radio for a short to ground or voltage. (Turn ON the ignition with 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 54

Go to Step 36

36

Replace the MSM. Refer to Memory Seat Control Module Replacement in Seats.

Did you complete the repair?

Go to Step 54

--

37
  1. Turn OFF the ignition.
  2. Disconnect the inflatable restraint sensing and diagnostic module (SDM).
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 38

Go to Step 40

38

Test the class 2 serial data circuit between the SDM and the following component:

    • The MSM (w/A45)
    • The radio (w/o A45)

for a short to ground or voltage. (Turn ON the ignition with 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 54

Go to Step 39

39

Replace the SDM. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement in SIR.

Did you complete the repair?

Go to Step 54

--

40

Is the vehicle equipped with F45?

Go to Step 41

Go to Step 43

41
  1. Turn OFF the ignition.
  2. Disconnect the continuously variable road sensing suspension (CVRSS) module.
  3. SDM).
  4. Turn ON the ignition with the engine OFF.
  5. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 42

Go to Step 43

42

Replace the CVRSS module.

Did you complete the repair?

Go to Step 54

--

43

Is the vehicle equipped with UQ4?

Go to Step 44

Go to Step 48

44
  1. Turn OFF the ignition.
  2. Disconnect the radio interface module (RIM).
  3. SDM).
  4. Turn ON the ignition with the engine OFF.
  5. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 45

Go to Step 48

45

Is the vehicle equipped with F45?

Go to Step 46

Go to Step 48

46

Test the class 2 serial data circuit between the CVRSS module and the RIM for a short to ground or voltage. (Turn ON the ignition with 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 54

Go to Step 47

47

Replace the RIM. Refer to Radio Speaker Amplifier Replacement in Entertainment.

Did you complete the repair?

Go to Step 54

--

48
  1. Turn OFF the ignition.
  2. Disconnect the remote function actuator (RFA) module.
  3. Turn ON the ignition with the engine OFF.
  4. Attempt to communicate with the body control module (PZM).

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 49

Go to Step 52

49

Is the vehicle equipped with F45 or UQ4?

Go to Step 50

Go to Step 51

50

Test the class 2 serial data circuit between the RFA module and the following component:

    • The CVRSS module (w/o UQ4)
    • The RIM (w/UQ4)

for a short to ground or voltage. (Turn ON the ignition with 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 54

Go to Step 51

51

Replace the RFA module. Refer to RFA Module Replacement in Keyless Entry.

Did you complete the repair?

Go to Step 54

--

52

Test the class 2 serial data circuit between the following:

    • The RFA module and the PZM
    • The EBCM and the PZM

for a short to ground or voltage. (Turn ON the ignition with 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 54

Go to Step 53

53

Replace the PZM. Refer to Body Control Module Replacement in Body Control System.

Did you complete the repair?

Go to Step 54

--

54
  1. Connect all of the disconnected modules.
  2. Connect any other disconnected connectors.
  3. Install a scan tool.
  4. Turn ON the ignition with the engine OFF.

    5. Important: The scan tool may require a power up reset before communication will occur. Turn off or disconnect the scan tool before you display DTCs.

  5. Wait for 10 seconds.
  6. 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 not have DTCs set.)
  7. 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 56

Go to Step 55

55

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

Go to Step 56

Go to Step 58

56

Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction. The PCM may have DTC(s) P1602 to P1615, or P1626 set. If only P1600 DTC(s) in the range specified along with history U1xxx DTC(s) are set and the vehicle will start and run, the action is complete.

Did you complete the action?

Go to Step 57

--

57

Did you diagnose all of the DTCs?

Go to Step 58

Go to Step 56

58

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

--