DTC Descriptors
DTC U0100 00: Lost Communication With Engine/Powertrain Control Module (ECM/PCM)DTC U0101 00: Lost Communication With Transmission Control Module (TCM)
DTC U0121 00: Lost Communication With Electronic Brake Control Module (EBCM)
DTC U0140 00: Lost Communication With Body Control Module (BCM)
DTC U2105 00: Lost Communications With Engine Control System (ECM/PCM)
DTC U2106 00: Lost Communications With Transmission Control System (TCM)
DTC U2108 00: Lost Communications With ABS/TCS Control System (EBCM)
DTC U2107 00: Lost Communications With Body Control System (BCM)
Diagnostic Fault Information
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Module positive voltage circuits | U0100- U0299 and U2105-U2199 | U0100- U0299 and U2105-U2199 | U0100- U0299 and U2105-U2199 | -- |
Module ground circuits | U0100- U0299 and U2105-U2199 | U0100- U0299 and U2105-U2199 | U0100- U0299 and U2105-U2199 | -- |
Module High Speed GMLAN Serial Data circuits | U0100- U0299 and U2105-U2199 | U0100- U0299 and U2105-U2199 | U0100- U0299 and U2105-U2199 | -- |
1. Scan Tool Does Not Communicate with Low Speed GMLAN Device | ||||
Circuit/System 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.
Conditions for Running the DTC
| • | The system voltage is between 9-16 volts. |
| • | 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 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. |
Diagnostic Aids
| • | Use the DTC Descriptor list above to determine the module which is not communicating. |
| • | If there are multiple non-communicating modules choose the one closest to the data link connector (DLC). |
| • | 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 Speed GMLAN serial data providing the vehicle is equipped with the option that uses that module. |
Reference Information
Schematic Reference
Connector End View Reference
Master Electrical Component List
Electrical Information Reference
Circuit/System Testing
- Using the DTC Descriptor and Diagnostic Aids above, determine the module that is not communicating that should be tested.
- Ignition OFF, disconnect the harness connector of the module that is not communicating.
- Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.
- Test for less than 1 ohm of resistance between the module ground circuits and ground.
- If all circuits test normal, replace the module that is not communicating.
| ⇒ | 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. |
| ⇒ | If greater than 1 ohm, repair the open in the ground circuit. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for module replacement, setup, and programming |
