U2099

DTC U2099

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using the 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) 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) (F38) (F55)
* Distance sensing cruise control (DSCC) module - (K59)

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

Short to ground will also set multiple history no communication codes for GMLAN high speed modules

Circuit/System Testing

1. With the ignition OFF, disconnect the X 1 harness connector at the EBCM, DSCC, and ESC module 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 X 3 at the BCM.
3. With the X 1 harness connector at the EBCM, DSCC, and ESC modules disconnected, test for infinite resistance between the high speed GMLAN serial data wake up circuit terminal 19 and ground.

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

4. If all circuits test normal and DTC is current, replace the BCM.

Repair Instructions

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