Lost Communications With Steering Angle Sensor (SAS)

DTC U2105-U2199 (U2142 or U2143 only)

Diagnostic Instructions
^ Perform the [Diagnostic System Check - Vehicle Diagnostic Information] prior to using this diagnostic procedure.
^ Review [Strategy Based Diagnosis] for an overview of the diagnostic approach. Strategy Based Diagnosis
^ [Diagnostic Procedure Instructions - Vehicle Diagnostic Information] provides an overview of each diagnostic category. Diagnostic Procedure Instructions - Vehicle Diagnostic Information

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:

Diagnostic Fault Information

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] Programming and Relearning

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 - Vehicle Diagnostic Information] after completing the diagnostic procedure.
^ [GMLAN Wiring Repairs]
^ [Control Module References] for module replacement, setup, and programming Programming and Relearning