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U1500




DTC U1500

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 U1500 00
- Inter-device Dedicated Bus

Diagnostic Fault Information





Circuit/System Description

A private CAN bus is used to communicate information between the electronic brake control module, yaw and lateral accelerometer sensor, and steering angle sensor. The serial data is transmitted on two twisted wires that allow speeds up to 500 Kb/s. The twisted pair is terminated with two 120 ohm resistors, one is internal to the electronic brake control module (EBCM) and the other can be a separate resistor in a connector assembly or in another sensor. The resistors are used as the load for the bus during normal vehicle operation. If serial data is lost, electronic brake control module will set a no communication code against the non-communicating sensor. Note that a loss of serial data DTC does not represent a failure of the control module that set it.

Conditions for Running the DTC

* The system voltage is between 9-16 V.
* The vehicle power mode requires serial data communications.

Conditions for Setting the DTC

* A supervised periodic message that includes the transmitter module availability has not been received.
* Open, short to ground, or short to voltage on the serial data circuits.

Action Taken When the DTC Sets

* The EBCM disables the vehicle stability enhancement system (VSES) for the duration of the ignition cycle.
* A driver information center (DIC) message and/or a warning indicator may be displayed.

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 100, without a repeat of the malfunction.

Diagnostic Aids

* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of-communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

- A control module on the data communication circuit was disconnected while the communication circuit is awake.
- Power to one or more modules was interrupted during diagnosis
- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.
- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.
- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

* Do not replace a control module reporting a U code. The U code identifies which control module needs to be diagnosed for a communication issue.
* Ensure that all connections/connectors for the area of concern are fully seated.

Reference Information
Schematic Reference

* Data Communication Schematics (Electrical Diagrams)
* Antilock Brake System Schematics (Electrical Diagrams)

Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

Data Link Communications 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

Note: Each control module may need to be disconnected to isolate a circuit fault. Use the schematic to identify the following:

* Control module locations on the serial data circuits
* Each control module ignition circuit, ground circuit, and serial data circuit terminals

1. Ignition OFF, disconnect the harness connectors at the yaw and lateral accelerometer sensor.
2. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 10 ohm between the low reference circuit terminal 1 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance. If the circuit tests normal, replace the electronic brake control module (EBCM).

3. Ignition OFF, verify that a test lamp does not illuminate between the ignition circuit terminal 4 and ground.

• If the test lamp does illuminate, test the ignition circuit for a short to voltage. If the circuit tests normal, replace the EBCM.

4. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 4 and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the EBCM.

Note: To ensure that the following test steps work correctly, the harness connector at the steering angle sensor has to be disconnected.

5. Ignition OFF, disconnect the harness connectors at the EBCM and the steering angle sensor.
6. Ignition ON, test for less than 1 V between each yaw and lateral accelerometer sensor serial data circuit terminal listed below and ground.

* Serial data circuit terminal 2
* Serial data circuit terminal 3

• If greater than the specified range, test the appropriate serial data circuit for a short to voltage.

7. Ignition OFF, test for infinite resistance between each yaw and lateral accelerometer sensor serial data circuit terminal listed below and ground.

* Serial data circuit terminal 2
* Serial data circuit terminal 3

• If not the specified value, test the appropriate serial data circuit for a short to ground.

8. Test for infinite resistance between the yaw and lateral accelerometer sensor serial data circuit terminals 2 and 3.

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

9. Test for less than 2 ohm in each serial data circuit between the yaw and lateral accelerometer sensor and the EBCM.

* Serial data circuit terminal 2 at the yaw and lateral accelerometer sensor harness connector and serial data circuit terminal 19 at the EBCM harness connector.
* Serial data circuit terminal 3 at the yaw and lateral accelerometer sensor harness connector and serial data circuit terminal 18 at the EBCM harness connector.

• If greater than the specified range, test the appropriate serial data circuit for an open/high resistance.

10. If all circuits test normal, replace the yaw and lateral accelerometer sensor and verify that the DTC does not reset.

• If the DTC resets, replace the steering angle sensor.

11. Verify that the DTC does not reset.

• If the DTC resets, replace the EBCM.

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)
* Steering Angle Sensor Replacement (Removal and Replacement)
* Control Module References (Programming and Relearning)for control module replacement, programming and setup

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