U2103

DTC 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 Descriptor
DTC U2103
- 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.

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.
* 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.

Reference Information
Schematic Reference

Data Communication Schematics (Electrical Diagrams)
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

Control Module References (Programming and Relearning)for Scan Tool Information

Circuit/System Testing

1. With a scan tool, verify communication with 1 or more modules is present.

• If no communication is available refer to Scan Tool Does Not Communicate with Low Speed GMLAN Device (Scan Tool Does Not Communicate with Low Speed GMLAN Device).

2. Ignition OFF, disconnect the X4 harness connectors at the BCM.
3. Ignition OFF, test for less than 5 ohms of resistance between the ground circuit terminal E 12 and ground.

• If greater than the specified value, test the circuit for an open/high resistance.

4. Ignition OFF, disconnect the X1 harness connectors at the BCM.
5. Ignition OFF, test for less than 5 ohms of resistance between the ground circuit terminal 61 and ground.

• If greater than the specified value, test the circuit for an open/high resistance.

6. Reconnect the X1 and X4 harness connector and disconnect the X3 harness connector at the BCM.
7. Ignition ON, verify a test lamp illuminates between the B+ between the B+ circuit terminal D1 and ground.

• If test lamp does not Illuminate, test the circuit for a an open/high resistance. If the circuit fuse is open, test the circuit for a short to ground, if all circuits test normal, replace the BCM.

8. Ignition OFF, disconnect the harness connector of the non communicating module.
9. Ignition OFF, test for less than 5 ohms of resistance between the applicable modules ground circuit terminal and ground

• If greater than the specified value, test the circuit for an open/high resistance.

10. Ignition ON, verify a test lamp illuminates between the applicable modules B+ circuit and ground.

• If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance.

11. Individually disconnect the harness connectors at each control module on the GMLAN serial data line, beginning with the module furthest from the DLC as noted on the system schematic. After each disconnection, verify the scan tool is unable to communicate with the BCM.

• If the scan tool is able to communicate with the BCM, test the GMLAN serial data line at the most recently disconnected module.

12. If all circuits test normal, replace the applicable module.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* GMLAN Wiring Repairs (Component Tests and General Diagnostics)
* Control Module References (Programming and Relearning)for control module replacement, setup, and programming