U0123

DTC U0123

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



DTC Descriptor
DTC U0123 00
- Lost Communication With Chassis Control YRS System




Circuit/System Description

The run relay 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 electronic brake control module EBCM, supervisory control module (SCM), active front steering (AFS), yaw rate sensor, and the steering angle or steering wheel position 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 (Description and Operation) .


Conditions for Running the DTC

* Ignition is On, 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 is missing or invalid.


Action Taken When the DTC Sets

* The EBCM disables the VSES for the duration of the ignition cycle.
* The driver information center (DIC) displays the STABILITRAK Off message.
* The ABS/TCS remains functional.



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 SCM.
* Possible causes of this DTC are as follows:

- Inspect the mounting of the Yaw sensor to ensure proper orientation and installation of the sensor.
- On a level surface, read the Yaw sensor offset value to ensure a value within the proper range.




Reference Information
Schematic Reference

* Data Communication Schematics (Electrical Diagrams)
* Antilock Brake System Schematics (Except JL7) (Antilock Brake System Schematics (Except RPO JL7))Antilock Brake System Schematics (JL7) (Antilock Brake System Schematics (With RPO JL7))
* Control Module References (Programming and Relearning)

Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

ABS Description and Operation (Without JL7) (ABS Description and Operation (Without RPO JL7))ABS Description and Operation (With JL7) (ABS Description and Operation (With RPO JL7))
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information


Circuit/System Verification

With scan tool installed, clear the DTCs then drive the vehicle in a straight line at a speed greater than 20 km/h (13 mph). If the DTC did not set as a current DTC see Diagnostic Aids.


Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the yaw rate/lateral acceleration sensor.
2. Ignition OFF for 60 seconds, test for less than 5 ohms between the low reference circuit terminal 1 and ground.

• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the yaw rate/lateral acceleration sensor.

3. Ignition ON, test for ignition voltage between the ignition voltage circuit terminal 4 and ground.

• If not within the specified range, test the ignition voltage circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the yaw rate/lateral acceleration sensor.

4. Ignition OFF, disconnect the harness connector X3 at the SCM, and X3 at the EBCM.
5. Ignition ON, test for less than 1 volt between the following terminal listed below and ground.

* SCM serial data circuit terminal 52
* SCM serial data circuit terminal 72


• If greater than the specified value, test the appropriate serial data circuit for a short to voltage. If the circuit tests normal, replace the yaw rate/lateral acceleration sensor.

6. Ignition OFF, test for infinite resistance between the following terminal listed below and ground.

* SCM serial data circuit terminal 52
* SCM serial data circuit terminal 72


• If not the specified value, test the appropriate serial data circuit for a short to ground. If the circuit tests normal, test or replace the yaw rate/lateral acceleration sensor

7. Test for less than 2 ohms between the appropriate serial data circuit terminals listed below.

* Serial data circuit terminal 52 at the SCM harness connector and terminal 2 at the yaw rate/lateral acceleration sensor harness connector.
* Serial data circuit terminal 72 at the SCM harness connector and terminal 3 at the yaw rate/lateral acceleration sensor harness connector.


• If greater than the specified range, test the appropriate serial data circuit for an open/high resistance. If the circuit tests normal, replace the yaw rate/lateral acceleration sensor.

8. Test for infinite resistance between the SCM serial data circuit terminal 52 and the SCM serial data circuit terminal 72.

• If not the specified value, repair the serial data circuits for a short together.

9. If all circuits test normal, replace the SCM.



Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* GMLAN Wiring Repairs (Component Tests and General Diagnostics)
* Vehicle Yaw Sensor with Vehicle Lateral Accelerometer Replacement (Yaw Sensor with Vehicle Lateral Accelerometer Replacement)
* Control Module References (Programming and Relearning) for module replacement, setup, and programming