GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saab 🢒 2007 🢒 9-7x 🢒 Power and Signal Distribution 🢒 Data Communications 🢒 DTC U0100-U0299

Circuit Description

Modules connected to the high and low speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC U0100 Lost Communication With Engine/Powertrain Control Module (ECM/PCM)
    • DTC U0101 Lost Communication With Transmission Control Module (TCM)

Conditions for Running the DTCs
    • Voltage supplied to the modules is in the normal operating voltage range.
    • The vehicle power mode requires serial data communication to occur.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

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
    • A poor connection at the inoperative module may cause this code to set.
    • An improperly powered module may cause this code to set.

Step

Action

Yes

No

Schematic Reference: LINK

Connector End View Reference: Master Electrical Component List

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Important: Use the DTC Descriptor list to determine the module which 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 circuits
    • The battery voltage output circuits
    • The switched battery positive voltage circuits

Refer to the following:

    •  Control Module References for the applicable schematic
    •  Circuit Testing
    •  Wiring Repairs

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:
    3. •  Control Module References for the applicable schematic

Did you find and correct the condition?

Go to Step 7

Go to Step 4

4

Test the high speed GMLAN serial data circuits of the module that is not communicating for an open. Refer to the following:

    •  Control Module References for the applicable schematic
    •  Circuit Testing
    •  GMLAN Wiring Repairs

Did you find and correct the condition?

Go to Step 7

Go to Step 5

5

Test the following circuits of the module that is not communicating for poor connections:

    • The battery positive voltage circuits
    • The battery voltage output circuits
    • The switched battery positive voltage circuits
    • The ground circuits
    • The high speed GMLAN serial data circuits

Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

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

--

7
  1. Reconnect all disconnected modules.
  2. Turn ON the ignition, with the engine OFF.
  3. Use the scan tool in order to clear the DTCs.

Does the scan tool still display any other current DTCs?

Go to Diagnostic System Check - Vehicle

System OK