Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC U2105: Lost Communication With Engine Control SystemDTC U2106: Lost Communications With Transmission Control System
DTC U2108: Lost Communications With ABS/TCS Control System
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Module B+ | U0100-U0299 | U0100-U0299 | -- | -- |
Ignition | U0100-U0299 | U0100-U0299 | -- | -- |
Module Ground | U0100-U0299 | U0100-U0299 | -- | -- |
Circuit/System Description
Modules connected to the controller area network (CAN) 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 messages exchanged on the serial data circuits. The supervised and periodic messages are used by the receiving module as an availability indicator from the transmitter module. Each message contains the identification number of the transmitting module. When a message indicates availability of the transmitting module is not received, the receiving module sets a DTC. A module with a CAN serial data circuits malfunction, or which loses power during the current ignition cycle, will set a Loss of Communication DTC by other modules requiring information from the failed module. The modules able to communicate will set a DTC Uxxxx indicating the module is not communicating. If any of the CAN circuits are shorted to battery voltage, ground or between them, no communication is possible on the CAN serial data bus, and the engine control module (ECM) sets a U2104 or U2100.
Conditions for Running the DTC
| • | The ignition is in the RUN position. |
| • | The system voltage is between 9-16 volts. |
Conditions for Setting the DTC
| • | A receiving module for the past 125 milliseconds did not detect the CAN serial data bus message from a transmitting module. |
| • | DTC U2100 is not present. |
| • | DTC B1365 is not present. |
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
| • | Use the DTC Descriptor list above to determine the module which is not communicating. |
| • | Some modules may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no module output voltage circuit is shorted to ground before replacing the module. |
| • | This diagnostic can be used for any module that should communicate with high or low speed GMLAN serial data providing the vehicle is equipped with the option that uses that module. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Circuit/System Testing
- Using the DTC Descriptor and Diagnostic Aids above, determine the module that is not communicating.
- Ignition OFF, disconnect the harness connector of the module that is not communicating.
- Test for less than 1 ohm between the module ground circuits and ground.
- Ignition ON, verify that a test lamp illuminates between all B+ circuits and ground.
- Verify that a test lamp illuminates between all ignition voltage circuits and ground.
- If all circuits test normal, replace the module that is not communicating.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | 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, also test the voltage outputs of the module for a short to ground. If the circuits test normal, replace the module. |
| ⇒ | 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, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the module. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for module replacement, setup, and programming |
