GM Service Manual Online
For 1990-2009 cars only
Table 1: The Control Module ID

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. 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 (SOH) monitoring/node alive messages. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. 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 no message is detected from a learned identification number for 5 seconds, a DTC U1XXX. XXX is equal to the 3-digit identification number of the module.

The control module ID number list provides a method for determining which module is not communicating. A module with an internal class 2 serial data circuit malfunction or which loses power during the current ignition cycle would have a lost communication DTC set by other modules. Use the control module ID number list in order to determine which module is not communicating and the lost communications with XXX diagnostic table in order to diagnose the malfunction. When no message is detected from a learned identification number for 5 seconds, a DTC U1XXX is set.

The Control Module ID

Control Module

ID Number

Powertrain/Engine Control Module (PCM/ECM)

016

Transfer Case Shift Control Module (TCSCM)

026

Electronic Brake Control Module (EBCM)

041

Body Control Module (BCM)

064

Inflatable Restraint Sensing and Diagnostic Module (SDM)

088

Instrument Panel Cluster (IPC)

096

Radio

128

DVD Player

133

Digital Radio Receiver (DRR)

137

Communication Interface Module (OnStar®)

151

HVAC Control Module

152

Driver Door Module (DDM)

160

Passenger Door Module (PDM)

161

Liftgate/Endgate Control Module (LGM/EGM)

162

Driver Seat Module (DSM)

166

HVAC Control Module - Rear Auxiliary

167

Power Roof Module (PRM)

173

Theft Deterrent Control Module (VTD)

192

When more than one loss of communication DTC is set in a single module or among multiple modules, diagnose the DTCs in the following order:

  1. Current DTCs before history DTCs except as specified in the diagnostic tables.
  2. The DTC which is reported the most times.
  3. From the lowest number DTC to the highest number DTC.

Conditions for Running the DTC

    •  Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.
    •  DTCs U1300, U1301 or U1305 do not have a current status.
    •  The vehicle power mode requires serial data communication to occur.

Conditions for Setting the DTC

A node alive message has not been received from an identified module within the last 5 seconds.

Action Taken When the DTC Sets

The module uses a default value for the missing parameter.

Conditions for Clearing the DTC

    • A current DTC clears when the malfunction is no longer present.
    • A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids

    • An intermittent open between a module and a star connector may cause this DTC to set.
    • A poor connection at a module or a star connector may cause this DTC to set.
    • An intermittent open in a star connector may cause this DTC to set.
    • An open voltage or ground circuit to a module may cause this DTC to set.
    • An internal module malfunction may cause this DTC to set.

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 Loss of Communication DTCs for those modules that 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

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

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:

    •  Control Module References for applicable schematics
    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 3

3

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

Refer to the following:

    •  Control Module References for applicable schematics
    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 4

4

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 7

Go to Step 5

5

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:

    •  Control Module References for applicable schematics
    •  Connector Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6

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 7

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7

  1. Install a scan tool.
  2. Turn ON the ignition 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 Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 8

8

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 Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 9

9

  1. Use the scan tool in order to clear the DTCs.
  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?

System OK

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