Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using the 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 U0100 00: Lost Communication With Engine/Powertrain Control Module (ECM/PCM)DTC U0101 00: Lost Communication With Transmission Control Module (TCM)
DTC U0104 00: Lost Communication With Cruise Control Module
DTC U0121 00: Lost Communication With Electronic Brake Control Module (EBCM)
DTC U0140 00: Lost Communication With Body Control Module (BCM)
DTC U0151 00: Lost Communication With Sensing and Diagnostic Module (SDM)
DTC U0155 00: Lost Communication With Instrument Panel Cluster (IPC) Control Module
DTC U0184 00: Lost Communication With Radio
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Class 2 Serial Data | 1 | U0100-U0299 | 1 | -- |
Battery Positive Voltage Circuits | U0100-U0299 | U0100-U0299 | -- | -- |
Ignition Voltage Circuits | U0100-U0299 | U0100-U0299 | -- | -- |
Module Ground Circuits | U0100-U0299 | U0100-U0299 | -- | -- |
1. Scan tool does not communicate with low speed GMLAN device | ||||
Circuit/System Description
Modules connected to the high and class 2 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). |
| • | Use Data Link References to determine if the module uses high speed or class 2 serial data communications |
| • | 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 class 2 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
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.
Terminal and connector identifiers will be different depending on the individual module being tested. Use Schematic Reference and Connector End View Reference to determine which connector and terminal to access.- Using the DTC Descriptor and Diagnostic Aids, determine the module that is not communicating that should be tested.
- Ignition OFF, disconnect the harness connector of the module that is not communicating.
- Test for less than 5 ohms of resistance between the module ground circuits and ground.
- Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.
- Verify that a test lamp illuminates between all ignition voltage circuits and ground.
- 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 all circuits test normal, replace the module that is not communicating.
| ⇒ | If greater than the specified range, test the ground circuit for an open. |
| ⇒ | If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM. |
| ⇒ | 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 faulty 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 faulty module. |
| ⇒ | If greater than the specified range, test the GMLAN serial data circuit(s) for open/high resistance. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for module replacement, setup, and programming |
