U2105

DTC U0100-U0299 or U2105-U2199

DIAGNOSTIC INSTRUCTIONS
- Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
- Review Strategy Based Diagnosis for an overview of the diagnostic approach.
- Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC DESCRIPTORs

DTC U0100
Lost Communication With Engine/Powertrain Control Module (ECM/PCM)

DTC U0101
Lost Communication With Transmission Control Module (TCM)

DTC U0121
Lost Communication With Electronic Brake Control Module (EBCM)

DTC U0140
Lost Communication With Body Control Module (BCM)

DTC U0198
Lost Communication With Communication Interface Module (OnStar(r))

DTC U2105
Lost Communication With Engine Control Module (ECM)

DTC U2106
Lost Communication With Transmission Control Module (TCM)

DTC U2107
Lost Communication With Body Control Module (BCM)

DTC U2108
Lost Communication With Electronic Brake Control Module (EBCM)

DTC U2112
Lost Communication With Electronic Suspension Control (ESC) Module

DTC U2150
Navigation Electronic Control Unit (ECU) Gateway Communications

CIRCUIT/SYSTEM DESCRIPTION
Modules connected to the high 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. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.

CONDITIONS FOR RUNNING THE DTC
- Voltage supplied to the modules is in the normal operating voltage range.
- The vehicle power mode requires serial data communication to occur.
- The DTC U2100 does not have a current status.

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
Diagnose any power moding DTCs prior to diagnosing data communication DTCs

CIRCUIT/SYSTEM VERIFICATION

IMPORTANT: If more than one module is not communicating use Data Communication Schematics to determine which module is closest to the DLC. Start diagnostics with that module.

CIRCUIT/SYSTEM TESTING
1. With a scan tool, verify DTC B1440 is not set.
- If DTC is current refer to DTC B1440. B1440
2. Ignition OFF, disconnect the harness connector of the module that is not communicating.
3. Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.
- If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.
4. Verify that a test lamp illuminates between all ignition voltage circuits and ground.
- If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.
5. Test for less than 1 ohm of resistance between the module ground circuits and ground.
- If greater than 1 ohm, repair the ground circuit for an open.
6. Test for less than 1 ohm of resistance in the GMLAN serial data circuit(s) between the non-communicating module and the module that displays the DTC.
- If greater than 1 ohm of resistance, test the GMLAN serial data circuit(s) for open/high resistance.
7. If all circuits test normal, replace the module that is not communicating.

REPAIR INSTRUCTIONS
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

Control Module References for module replacement, setup, and programming. Programming and Relearning