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 U0122 00: Lost Communication With Vehicle Dynamics Control Module
DTC U0132 00: Lost Communication With Ride Level Control Module
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 U0159 00: Lost Communication With Parking Assist Control Module A
DTC U0164 00: Lost Communication With HVAC Control Module
DTC U0168 00: Lost Communication With Vehicle Theft Deterrent (VTD) Control Module
DTC U0170 00: Lost Communication With Passenger Presence System (PPS)
DTC U0184 00: Lost Communication With Radio
DTC U0186 00: Lost Communication With Audio Amplifier
DTC U0194 00: Lost Communication With Digital Radio Receiver (DRR)
DTC U0198 00: Lost Communication With Communication Interface Module (OnStar®)
DTC U0199 00: Lost Communication With Door control Module A
DTC U0200 00: Lost Communication With Door control Module B
DTC U0209 00: Lost Communication With Heated Seat Module (HSM)
DTC U0214 00: Lost Communication With Remote Function Actuator (RFA)
DTC U0241 00: Lost Communication With Headlamp Control Module A
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Low Speed GMLAN 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 | -- | -- |
Accessory Wake Up Serial Data | U1814 | U0100-U0299 | -- | -- |
High Speed GMLAN Serial Data Wake Up | U2099 | U0100-U0299 | -- | -- |
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.
The body control module (BCM) activates the high speed GMLAN serial data wake up and the accessory wake up serial data circuits by applying voltage when the ignition key is in ACC, ON or START. The high speed GMLAN serial data wake up circuit wakes up the electronic brake control module (EBCM) for bus communication and the accessory wake up serial data circuit wakes up the engine control module (ECM) and transmission control module (TCM).
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 or low speed GMLAN 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 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
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 2 ohms of resistance between the module ground circuits and ground.
- 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.
- 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 specified, repair the ground circuit for an open. |
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 5.
| ⇒ | 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, 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 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 specified, 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 |
