U0078

DTC U0078

Diagnostic Instructions

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

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

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

DTC Descriptor

DTC U0078 00
- Control Module Low Speed Communication Bus Off Malfunction

Circuit/System Description

The low speed GMLAN serial data bus is used to communicate information between the devices. The serial data is transmitted over a single wire to the appropriate devices. The low speed GMLAN serial data circuits also connect directly to the data link connector (DLC).

Conditions for Running the DTC

* Supply voltage to the devices are in the normal operating range.

* The vehicle power mode requires serial data communications.

Conditions for Setting the DTC

The device setting the DTC has attempted to establish communications on the serial data circuits more than 3 times in 5 seconds.

Action Taken When the DTC Sets

* The device suspends all message transmission.

* The device uses default values for all parameters received on the serial data circuits.

* The device 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 device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Circuit/System Verification

Diagnosis is accomplished using the symptom. Refer to Scan Tool Does Not Communicate with Low Speed GMLAN Device Scan Tool Does Not Communicate with Low Speed GMLAN Device.