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 Descriptor
DTC U2099 00: High Speed Communication Enable CircuitDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Serial Data Communication Enable | U2099, U0100-U0299¹ | U0100-U0299 | U0100-U0299² | -- |
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 ignition key is in ACC, ON or START. The serial data communication enable circuit wakes up the modules for serial data 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. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the appropriate module.
- Retest for current DTCs. DTC U2099 should remain current.
- Ignition OFF, disconnect the X 4 harness connector at the K9 BCM.
- Test for infinite resistance between the serial data communication enable circuit terminal 23 and ground.
- If all circuits tests normal, replace the K9 BCM.
| ⇒ | If the DTC becomes history, replace the appropriate module. |
| ⇒ | If less than infinite resistance, repair the enable circuit for a short to ground. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for module replacement, setup, and programming
