U2099

DTC U2099

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using the 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 U2099 00
- High Speed Communication Enable Circuit

Diagnostic Fault Information





Circuit/System Description

The body control module (BCM) applies voltage to the high speed GMLAN serial data wake up circuit, when the ignition key is in ACC, ON or START to enable several modules for bus communication.

Depending on option content, modules that may receive the signal are as follows:

* Electronic brake control module (EBCM)
* Electronic suspension control (ESC) module
* Distance sensing cruise control (DSCC) module
* Trailer brake control module
* Fuel pump flow control module
* Power take off module

Conditions for Running the DTC

* The system voltage is between 9-16 volts.
* The BCM attempts to enable the modules connected to the high speed GMLAN serial data wake up circuit.

Conditions for Setting the DTC

The BCM senses a short to ground or an open/high resistance on the high speed GMLAN serial data wake up circuit.

Action Taken When the DTC Sets

* The output command is turned off while the malfunction is present.
* The modules use a default value for the missing parameters.
* The modules is never signaled, therefore the specific subsystems will not function.

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

* Short to ground or an open/high resistance will also set multiple history no communication codes for GMLAN high speed modules
* Module terminal tension should be checked before any module is replaced.

Reference Information
Schematic Reference

* Body Control System Schematics (Electrical Diagrams)
* Data Communication Schematics (Electrical Diagrams)

Connector End View Reference

Component Connector End Views (Connector Views)
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

1. With the ignition OFF, disconnect the harness connector at each module on the circuit one at a time. After each disconnect, retest for current DTCs. DTC U2099 should remain current.

• If the DTC becomes history, replace the module disconnected before the DTC became history.

2. Ignition OFF, disconnect the harness connector X3 at the BCM.
3. With the harness connector at the modules disconnected, test for infinite resistance between the BCM high speed GMLAN serial data wake up circuit terminal X3, 19 and ground.

• If less than the specified value, test the wake up circuit for a short to ground.

4. Test for less than 1 ohm between the BCM high speed GMLAN serial data wake up circuit terminal X3, 19 and each serial data wake up circuit terminal at each disconnected module connector.

• If greater than the specified value, test for an open/high resistance in the serial data wake up circuit. If all circuits test normal and the DTC is current, replace the BCM.

Repair Instructions

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

Control Module References (Programming and Relearning) for module replacement, setup, and programming