U0107

DTC U0100-U02FF

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure, Diagnostic System Check - Vehicle

DTC Descriptors

DTC U0100 00: Lost Communication with Engine Control Module (ECM)
DTC U0101 00: Lost Communication with Transmission Control Module (TCM)
DTC U0107 00: Lost Communication with Throttle Actuator Control Module
DTC U0121 00: Lost Communication with Electronic Brake Control Module (EBCM)
DTC U0140 00: Lost Communication with Body Control Module

Diagnostic Fault Information






Circuit/System Description

Control 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 control modules. The control 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 V.
- The vehicle power mode master 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 control modules is never signaled. Therefore, the specific subsystems will not function.

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

- Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:
- A control module on the data communication circuit was disconnected while the communication circuit is awake.
- Power to one or more control modules was interrupted during diagnosis.
- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.
- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.
- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
- Use the DTC Descriptor list above to determine the control module which is not communicating.
- Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.
- Use Data Link References to determine if the control module uses high or low speed GMLAN serial data communications, Scan Tool Testing and Procedures
- Some control 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 control module output voltage circuit is shorted to ground before replacing the control module.
- This diagnostic can be used for any control module that should communicate with high or low speed GMLAN serial data providing the vehicle is equipped with the option that uses that control module.

Reference Information

Schematic Reference

- Data Link Connector Schematics, [1][2]Electrical Diagrams
- Control Module References, Control Module References

Connector End View Reference

- Master Electrical Component List, Connector Views

Description and Operation

- Data Link Communications Description and Operation, Data Link Communications

Electrical Information Reference

- Circuit Testing, Circuit Testing
- Connector Repairs, Connector Repairs
- Testing for Intermittent Conditions and Poor Connections, Testing For Intermittent Conditions and Poor Connections
- Wiring Repairs, Wiring Repairs

Circuit/System Testing

Note: Use the schematic to identify the following:

- Control modules the vehicle is equipped with.
- Control module locations on the low and high speed GMLAN serial data circuits.
- The control module's ground, B+, ignition, and serial data circuit terminals.

1. Using the DTC Descriptor above, determine the control module that is not communicating and should be tested.
2. Ignition OFF, disconnect the harness connector of the control module that is not communicating.
3. Test for less than 10 ohms between each ground circuit terminal and ground.
-> If greater than the specified range, test the ground circuit for an open/high resistance.
4. If equipped, ignition ON, verify that a test lamp illuminates between each B+ circuit terminal and ground.
-> If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.
5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.
6. Ignition OFF for 60 seconds, test for less than 5 ohms between the serial data circuit terminals and the appropriate data link connector (DLC) terminal listed below:
- Class 2 serial data circuit terminal 2
- Low speed GMLAN serial data terminal 1
- High speed GMLAN serial data terminal 6 or 14
-> If greater than the specified range, test the serial data circuit for an open/high resistance between the non-communicating control module and the control module setting the DTC or a serial data splice pack.
7. If all circuits test normal, replace the control module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.
- GMLAN Wiring Repairs, GMLAN Wiring Repairs
- Control Module References for control module replacement, programming and setup, Control Module References