Service Information

Volt

DTC U2099

Diagnostic Instructions

•	Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

•	Review Strategy Based Diagnosis for an overview of the diagnostic approach.

•	Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC U2099 00: High Speed Communication Enable Circuit

DTC U2099 01: High Speed Communication Enable Circuit Short to Battery

DTC U2099 02: High Speed Communication Enable Circuit Short to Ground

DTC U2099 04: High Speed Communication Enable Circuit Open

DTC U2099 5A: High Speed Communication Enable Circuit Not Plausible

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Serial Data Communication Enable	U2099, U0100-U02FF¹	U0100-U02FF	U0100-U02FF²	-
¹ Vehicle will not start. ² History only. If cleared the DTC will return after several ignition cycles.

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Serial Data Communication Enable

U2099, U0100-U02FF¹

U0100-U02FF

U0100-U02FF²

¹ Vehicle will not start.

² History only. If cleared the DTC will return after several ignition cycles.

Circuit/System Description

The body control module (BCM) activates the serial data communication enable circuit, when the vehicle is ON. The serial data communication enable circuit wakes up the control modules for serial data bus 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 control modules use a default value for the missing parameters until the next ignition cycle.

•	The control module(s) is never signalled, 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

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Circuit/System Testing

Note: Use the schematic to determine which control modules are on the BCM serial data communications enable circuit 23, X4.

Vehicle OFF, disconnect the harness connector at the most easily accessible control module on the K9 BCM serial data communication enable circuit.
Vehicle in Service Mode, retest for current DTCs. DTC U2099 should remain current.

⇒	If the DTC becomes history, replace the control module that was just disconnected.

With the prior control modules disconnected, repeat steps 1 and 2 for each control module on the circuit except the K9 BCM.
Vehicle OFF, disconnect the X4 harness connector at the K9 BCM.
Test for infinite resistance between the serial data communication enable circuit terminal 23 X4 and ground.

⇒	If less than infinite resistance, repair the serial data communication enable circuit for a short-circuit to earth.

If all circuits tests normal, replace the K9 BCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for module replacement, setup, and programming