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U1827




DTC U1826 or U1827

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 Descriptors
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

* 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 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 ([1][2]Antilock Brakes / Traction Control Systems)
* 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 (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 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 reference) 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. If the circuit tests normal, replace the EBCM.

5. Test for less than 1 ohm in the CAN bus serial data circuits between the Yaw Rate Sensor and the EBCM.

• If greater than 1 ohm, test the serial data circuits terminals 2 and 3 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 reference) circuit terminal 2 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 1 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 and the Yaw Rate Sensor.

• If greater than 1 ohm, test the serial data circuits terminals 3 and 4 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 (Component Tests and General Diagnostics)
* Vehicle Yaw Sensor with Vehicle Lateral Accelerometer Replacement (Service and Repair)
* Steering Wheel Position Sensor or Steering Shaft Lower Bearing Replacement (Steering Wheel Position Sensor or Steering Shaft Lower Bearing Replacement)
* Control Module References (Programming and Relearning) for module replacement, setup, and programming

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