For 1990-2009 cars

## DTC U0100-U0299 or U2105-U2199 Except U2142 or U2143

### 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 U0100: Lost Communication With Engine/Powertrain Control Module (ECM/PCM)
DTC U0101: Lost Communication With Transmission Control Module (TCM)
DTC U0121: Lost Communication With Electronic Brake Control Module (EBCM)
DTC U0140: Lost Communication With Body Control Module (BCM)
DTC U0198: Lost Communication With Communication Interface Module (OnStar®)
DTC U2105: Lost Communication With Engine Control Module (ECM)
DTC U2106: Lost Communication With Transmission Control Module (TCM)
DTC U2107: Lost Communication With Body Control Module (BCM)
DTC U2108: Lost Communication With Electronic Brake Control Module (EBCM)
DTC U2113: Lost Communication With Sensing Diagnostic Module (SDM)
DTC U2122: Lost Communication With Radio
DTC U2125: Lost Communication With Mobile Communications Control Systems
DTC U2137: Lost Communication With Vehicle Theft Deterrent (VTD)
DTC U2172: Lost Communication With Digital Radio Receiver

### Circuit/System Description

Modules connected to the 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 programmed information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are also supervised and some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module. When a message that indicates the availability of the transmitter module is not received, the receiver module sets a DTC against the transmitter module.

The DTC descriptors listed above provide a method for determining which module is not communicating. A module with a GMLAN serial data circuit malfunction or which loses power during the current ignition cycle will have a Loss of Communication DTC set by other modules that depend on information from that failed module. The modules that can communicate will set a DTC indicating the module that cannot communicate.

### Conditions for Running the DTC

• | Voltage supplied to the modules is in the normal operating voltage range.

• | The vehicle power mode requires serial data communication to occur.

• | The DTC U2100 does not have a current status.

### 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 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

Diagnose any power moding DTCs prior to diagnosing data communication DTCs.

### Reference Information

#### Schematic Reference

Data Communication Schematics

#### Connector End View Reference

Data Communication Connector End Views

#### Description and Operation

Data Link Communications Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Output Controls

• | Scan Tool Data List

• | Scan Tool Data Definitions

### Circuit/System Testing

Important: If more than one module is not communicating , refer to Data Communication Schematics to determine which module is closest to the DLC. Start diagnostics with that module.

1. Ignition OFF, disconnect the harness connector of the module that is not communicating.
2. Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.

⇒ | 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.

3. Verify that a test lamp illuminates between all ignition voltage circuits and ground.

⇒ | 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.

4. Test for less than 1 ohm of resistance between the module ground circuits and ground.

⇒ | If greater than 1 ohm, repair the ground circuit for an open.

5. Test for less than 1 ohm of resistance in the GMLAN serial data circuits between the non-communicating module and the module that displays the DTC.

⇒ | If greater than 1 ohm of resistance, test the GMLAN serial data circuits for open/high resistance.

6. If all circuits test normal, replace the module that is not communicating.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for module replacement, setup and programming

## DTC U0100-U0299 or U2105-U2199 U2142 or U2143 only

### 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 U2142 00: Lost Communication With Yaw Rate Sensor (YRS)
DTC U2143 00: Lost Communications With Steering Angle Sensor (SAS)

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
CAN Bus High Serial Data | U1500 | U2105-U2199 (U2142 or U2143 only) | U1500 | --
CAN Bus Low Serial Data | U1500 | U2105-U2199 (U2142 or U2143 only) | U1500 | --
CAN Bus High Terminated Serial Data | U1500 | U2105-U2199 (U2142 or U2143 only) | U1500 | --
CAN Bus Low Terminated Serial Data | U1500 | U2105-U2199 (U2142 or U2143 only) | U1500 | --
Module Voltage Circuits | U2105-U2199 (U2142 or U2143 only) | U2105-U2199 (U2142 or U2143 only) | -- | --
Module Ground Circuits | -- | U2105-U2199 (U2142 or U2143 only) | -- | --

### Circuit/System Description

Modules connected to the CAN bus serial data circuits are high speed serial data modules that 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. 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 electronic brake control module (EBCM) activates the other modules connected to the CAN serial data circuits by applying voltage when the ignition key is in ACC, ON or START. The EBCM, Yaw Rate Sensor, and the Steering Angle Sensor are the only modules connected to the CAN bus serial data circuits. For more information on CAN bus serial data refer to Data Link Communications Description and Operation .

### Conditions for Running the DTC

• | The system voltage is between 9-16 volts.

• | 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 Vehicle stability Enhancement System (VSES), if equipped, and Traction Control System (TCS) will not function.

• | System OFF lamps will illuminate for these systems.

### 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.

• | If there are multiple non-communicating modules choose the one closest to the EBCM.

### Reference Information

#### Schematic Reference

• | Data Communication Schematics

• | Control Module References

#### Connector End View Reference

Master Electrical Component List

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

### Circuit/System Testing

1. Using the DTC Descriptor and Diagnostic Aids above, determine the module that is not communicating that should be tested.
2. Ignition OFF, disconnect the harness connector of the module that is not communicating.
3. Ignition ON, verify that a test lamp illuminates between the module voltage circuit and ground.

⇒ | If the test lamp does not illuminate, repair the circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the EBCM.

4. Test for less than 5 ohm of resistance between the module ground circuits and ground. If the circuit tests normal, replace the EBCM.

⇒ | If greater than 5 ohm, repair the ground circuit for an open.

5. Test for less than 1 ohm of resistance in the CAN bus serial data circuits between the non-communicating module and the EBCM.

⇒ | If greater than 1 ohm of resistance, test the serial data circuit for open/high resistance.

6. If all circuits test normal, replace the module that is not communicating.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | GMLAN Wiring Repairs

• | Control Module References for module replacement, setup, and programming