For 1990-2009 cars

## DTC U2105-U2199 Except U2142 and 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 U2105 00: Lost Communication With Engine Control System
DTC U2106 00: Lost Communications With Transmission Control System
DTC U2107 00: Lost Communications With Body Control System

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Module Voltage Circuits (input or output) | U2105-U2199 Except U2142 and U2143 | U2105-U2199 Except U2142 and U2143 | -- | --
Module Ground Circuits | -- | U2105-U2199 Except U2142 and U2143 | -- | --

### Circuit/System Description

Modules connected to the high 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 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 module(s) is never signaled, therefore the specific subsystem(s) 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

• | 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.

### 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 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.

4. 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.

5. 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.

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

• | GMLAN Wiring Repairs

## DTC 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