U0002

DTC U0002

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 U0002
- High Speed Communication Bus Performance




Circuit/System Description

The high speed GMLAN serial data circuits are high speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. The high speed GMLAN serial data circuits also connect directly to the data link connector (DLC).


Conditions for Running the DTCs

* Supply voltage to the modules are in the normal operating range.
* The vehicle power mode requires serial data communications.



Conditions for Setting the DTC

The module setting the DTC has attempted to establish communications on the GMLAN circuits more than 3 times.


Action Taken When the DTCs Sets

* The module suspends all message transmission.
* The module uses default values for all parameters received on the serial data circuits.
* The module inhibits the setting of all other communication DTCs.



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

* An intermittent condition is likely to be caused by a short on the high speed GMLAN serial data circuits.
* This DTC cannot be retrieved with a current status. Diagnosis is accomplished using the symptom Scan Tool Does Not Communicate with High Speed GMLAN Device (Scan Tool Does Not Communicate with High Speed GMLAN Device) .
* Refer to Data Link References (Data Link References) for the specific modules using high speed GMLAN serial data.



Reference Information
Schematic Reference

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)

Scan Tool Reference

Control Module References (Programming and Relearning)for scan tool information.