GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2005 🢒 Sunfire 🢒 Brakes 🢒 Hydraulic Brakes 🢒 DTC U1001-U1254

Circuit Description

Each module connected to the class 2 serial data circuit monitors serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for state of health monitoring. Once an identification number is learned by a module, it will monitor for that modules node alive message. Each module on the class 2 serial data circuit is required to send a node alive message every 2 seconds. When a control module does not detect a node alive message from a learned identification number for 5 seconds, DTC U1001-U1254 will set.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC U1016 Lost Communications With Engine Control System (PCM)
    • DTC U1040 Lost Communications With Electronic Brake Control Module (EBCM)
    • DTC U1064 Lost Communications With Body Control Module (BCM)
    • DTC U1088 Lost Communications With Restraints Control System (SDM)
    • DTC U1096 Lost Communications With Instrument Panel Cluster (IPC)
    • DTC U1128 Lost Communications With Radio

Conditions for Running the DTC
    • The power mode is RUN.
    • The modules voltage supply is 9-16 volts.

Conditions for Setting the DTC

A message from a learned control module has not been detected for the past 5 seconds.

Conditions for Clearing the DTC
    • A current DTC will clear when a node alive message from the failed identification number is detected on the class 2 serial data circuit or at the end of the current ignition cycle.
    • A history DTC clears when the ignition is cycled 100 times without a repeat of the malfunction.

Diagnostic Aids
    • When more than one loss of communication DTC is set in either one module or in several modules, diagnose the DTCs in the following order:
       - Current DTCs before history DTCs, unless instructed otherwise in the diagnostic table.
       - The DTC which is reported the most times.
       - From the lowest number DTC to the highest number DTC.
    • When multiple loss of communication DTCs are set, the cause is likely to be two opens in the class 2 serial data circuit. Use the class 2 serial data circuit schematic in order to determine the location of the opens. Refer to Data Link Connector Schematics .

Test Description

The number below refers to the step number on the diagnostic table.

  1. The module which was not communicating on the class 2 serial data circuit may have set the Loss of Communication DTCs for the modules it was monitoring.

Step

Action

Yes

No

Schematic Reference: Data Link Connector Schematics

Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views in Wiring Systems.

1

Important: Use the control module ID number list in order to determine which module is not communicating.

Test the following circuits of the module that is not communicating for an open or a short to ground:

    • The battery positive voltage input circuits
    • The battery positive voltage output circuits
    • The ignition voltage input circuits
    • The ignition voltage output circuits
    • The switched battery positive voltage circuits

Refer to the following:

    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 6

Go to Step 2

2
  1. Turn the ignition OFF.
  2. Test the ground circuits of the module that is not communicating for an open.

Refer to the following:

    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 6

Go to Step 3

3

Test the class 2 serial data circuits of the module that is not communicating for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 6

Go to Step 4

4

Inspect the harness connectors of the module that is not communicating for poor connections and terminal tension at the following circuits:

    • The battery positive voltage input circuits
    • The battery positive voltage output circuits
    • The ignition voltage input circuits
    • The ignition voltage output circuits
    • The switched battery positive voltage supply circuits
    • The ground circuits
    • The class 2 serial data circuits

Refer to the following:

    •  Connector Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 6

Go to Step 5

5

Replace the module that is not communicating. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 6

--

6

  1. Install a scan tool.
  2. Turn the ignition ON, with the engine OFF.
  3. Select the Display DTCs function for the module which was not communicating.

Does the scan tool display any DTCs which do not begin with a "U"?

Go to Control Module References

Go to Step 7

7

Select the Display DTCs function for the modules which had the Loss of Communications DTC set.

Does the scan tool display any DTCs which do not begin with a "U"?

Go to Control Module References

Go to Step 8

8
  1. Clear the DTCs with the scan tool.
  2. Continue diagnosing or clearing the DTCs until all the modules have been diagnosed and all the DTCs have been cleared.

Did you complete the action?

Go to Control Module References

--