U2099

DTC U2099

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* 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) activates the serial data communication enable circuit, when the ignition key is in ACC, ON or START. The serial data communication enable circuit wakes up the electronic brake control module (EBCM) for buss communication.

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

The BCM senses a short to ground on the serial data communication enable 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 until the next ignition cycle.
* 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.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the EBCM.
2. Retest for current DTCs. DTC U2099 should remain current.

^ If the DTC becomes history, replace the EBCM.

3. Ignition OFF, disconnect the X 3 harness connector at the BCM.
4. Test for infinite resistance between the serial data communication enable circuit terminal 19 and ground.

^ If less than infinite resistance, repair the enable circuit for a short to ground.

5. If all circuits tests normal, replace the BCM.

Repair Instructions

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