U2099

DTC U2099

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 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 - (FE1) (F55)



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 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 module(s) is never signaled, therefore the specific subsystem(s) will not function.
* The vehicle will not start while the circuit is shorted to ground.



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 DMM MIN/MAX function to capture/locate intermittent conditions.
* Short to ground will also set multiple history no communication codes for GMLAN high speed modules.



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 (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)



Circuit/System Testing

1. With the ignition OFF, disconnect the harness connector at the EBCM and ESC module one at a time. After each disconnect, clear the DTC, cycle the ignition key 3 times, then retest for the DTC. DTC U2099 should reset.

• If the DTC does not reset, replace the last module disconnected.

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

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

4. If all circuits test normal, 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