You need to find and correct why at least 1 controller is missing from the on-board network as the U2103 DTC is a COMM code
Could be a bad wire or wiring pin of a controller that connects to the network
U2103
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (
Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (
Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (
Initial Inspection and Diagnostic Overview)provides an overview of each diagnostic category.
DTC Descriptors
DTC U02103
- Fewer Controllers On Than Programmed
Circuit/System Description
Modules connected to the 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 programmed information about what messages are needed to be exchanged on the serial data circuits, for each virtual network.
The messages are also supervised, and some periodic messages are used by the receiver module as an availability indication of the transmitter module. DTC U2103 will set when fewer modules are detected on the buss before the modules can learn the other module's IDs. If the communication buss is opened, or if a module's power supply is lost when the vehicle is in the OFF power mode, and then placed in the RUN power mode, U2103 will set in specific modules.
Conditions for Running the DTC
* The system voltage is between 9-16 volts.
* The vehicle power mode requires serial data communication to occur.
* 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 parameters.
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 of 50, without a repeat of the malfunction.
Reference Information
Schematic Reference
Control Module References (
Programming and Relearning)
Connector End View Reference
Component Connector End Views (
Connector Views)
Description and Operation
Data Link Communications Description and Operation (
Description and Operation)
Electrical Information Reference
* Circuit Testing (
Component Tests and General Diagnostics)
* Connector Repairs (
Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (
Component Tests and General Diagnostics)
* Wiring Repairs (
Component Tests and General Diagnostics)
Scan Tool References
Data Link Communications Description and Operation (
Description and Operation)for Scan Tool information.
Circuit/System Testing
Important: If more than one module is not communicating use Data Communication Schematics (
Electrical Diagrams)
to determine which module is closest to the DLC. Start diagnostics with that module.
1. Using the DTC Descriptor and Diagnostic Aids above, determine the module that is not communicating that should be tested.
2. Ignition OFF, disconnect the harness connector of the module that is not communicating.
Important: Only the high speed GMLAN modules have a wired serial data wake up circuit. Refer to the module schematics to identify which modules have a wake-up circuit.
If the module that is not communicating does not have a serial data wake up circuit, proceed to step 4.
3. Ignition ON, verify that a test lamp illuminates between the high speed GMLAN serial data wake up circuit OR the accessory wake up serial data circuit and ground.
• If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.
4. Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.
• If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.
5. Verify that a test lamp illuminates between all ignition voltage circuits and ground.
• If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.
6. Test for less than 1 ohm of resistance between the module ground circuits and ground.
• If greater than 1 ohm, test the ground circuit for an open.
7. 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.
8. If all circuits test normal, replace the module that is not communicating.
Repair Instructions
Perform the Diagnostic Repair Verification (
Verification Tests) after completing the diagnostic procedure.
* Control Module References (
Programming and Relearning)for module replacement, setup, and programming
* GMLAN Wiring Repairs (
Component Tests and General Diagnostics)
