U0074

DTC U0074

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 U0074 00
- Control Module Communication Bus B Off

Diagnostic Fault Information






Circuit/System Description

The high speed hybrid GMLAN serial data circuits are serial data buses used to communicate information between the control modules. The serial data circuits also connect directly to the data link connector (DLC) for programming purposes.

Conditions for Running the DTCs

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

Conditions for Setting the DTC

The module setting the DTC has attempted to establish communications on the high speed hybrid GMLAN serial data 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, without a repeat of the malfunction.

Diagnostic Aids

* An intermittent condition is likely to be caused by a short on the high speed hybrid GMLAN serial data circuits.
* Refer to Data Link References to determine which serial data system is used for a specific module. Data Link References

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair. Verification Tests