U1826
DTC U1826 or U1827
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
DTC Descriptor
DTC U1826 71
- Lost Communication With Multi-Axis Acceleration Sensor Module on Bus "B" Invalid Serial Data Received
DTC U1826 72
- Lost Communication With Multi-Axis Acceleration Sensor Module on Bus "B" Alive Counter Incorrect/Not Updated
DTC U1826 7F
- Lost Communication With Multi-Axis Acceleration Sensor Module on Bus "B" Erratic
DTC U1827 71
- Lost Communication With Steering Angle Sensor Module on Bus "B" Invalid Serial Data
DTC U1827 72
- Lost Communication With Steering Angle Sensor Module on Bus "B" Alive Counter Incorrect/Not Updated
DTC U1827 74
- Lost Communication With Steering Angle Sensor Module on Bus "B" Value of Signal Protection Calculation Incorrect
DTC U1827 7F
- Lost Communication With Steering Angle Sensor Module on Bus "B" Erratic
Diagnostic Fault Information
Circuit/System Description
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 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 EBCM.
Reference Information
Schematic Reference
* Data Communication Schematics (Electrical Diagrams)
* Antilock Brake System Schematics (Electrical Diagrams)
* Control Module References (Programming and Relearning)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
ABS Description and Operation (Description and Operation)
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)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Testing
Yaw Rate Sensor DTC U1826
1. Use 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 at the Yaw Rate Sensor.
3. Ignition ON, verify that a test lamp illuminates between the Yaw Rate Sensor voltage (12-volt ref) circuit terminal 1 and ground.
• If the test lamp does not illuminate, test the circuit for a short to ground, or open/high resistance. If the circuit tests normal, replace the EBCM.
4. Ignition OFF, test for less than 5 ohms between the Yaw Rate Sensor low reference circuit terminal 6 and ground.
• If greater than the specified value, test the ground circuit for an open/high resistance.
5. Test for less than 1 ohm in the CAN bus serial data circuits between the Yaw Rate Sensor terminals 3 and 2, and the EBCM connector 21 and 33.
• If greater than 1 ohm, test the serial data circuits for open/high resistance.
6. If all circuits test normal, replace the yaw rate sensor.
Steering Wheel Position Sensor (Steering Angle Sensor) DTC U1827
1. Use 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 at the Steering Wheel Position Sensor.
3. Ignition ON, verify that a test lamp illuminates between the Steering Wheel Position Sensor voltage (12-volt ref) circuit terminal 5 and ground.
• If the test lamp does not illuminate, test the circuit for a short to ground, or open/high resistance. If the circuit tests normal, replace the Steering Wheel Position Sensor.
4. Ignition OFF, test for less than 5 ohms between the Steering Wheel Position Sensor low reference circuit terminal 6 and ground.
• If greater than the specified value, test the ground circuit for an open/high resistance. If the circuit tests normal, replace the Steering Wheel Position Sensor.
5. Test for less than 1 ohm in the CAN bus serial data circuits between the Steering Wheel Position Sensor terminal 2 and 3, and the Yaw Rate Sensor terminal 5 and 4.
• If greater than 1 ohm, test the serial data circuits for open/high resistance.
6. If all circuits test normal, replace the Steering Wheel Position Sensor.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* GMLAN Wiring Repairs (GMLAN Wiring Repairs)
* Vehicle Yaw Sensor with Vehicle Lateral Accelerometer Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for module replacement, setup, and programming