Circuit Description
Modules connected to the class 2 serial data circuit monitor for serial
data communications during normal vehicle operation. Operating information
and commands are exchanged among the modules. In addition to this, Node
Alive (State of Health) messages are transmitted by each module on the class
2 serial data circuit about once every two seconds. When the module detects
no messages and a low voltage on the class 2 serial data circuit for approximately
three seconds, U1300 is set and the setting of all other class 2 serial
communication DTCs is inhibited.
Conditions for Running the DTC
| • | The following diagnostic trouble codes do not have a current status: |
| • | The vehicle power mode (ignition switch position) requires serial
data communication to occur. |
Conditions for Setting the DTC
| • | No valid messages are detected on the class 2 serial data circuit. |
| • | The voltage level detected on the class 2 serial data circuit
is low. |
| • | The above conditions are met for approximately three seconds. |
Action Taken When the DTC Sets
| • | The module inhibits the setting of all other class 2 DTCs. |
| • | The module uses default values for all parameters received on
the class 2 serial data circuit. |
Conditions for Clearing the DTC
| • | A current U1300 will clear when a valid class 2 message is detected
on the class 2 serial data circuit or at the end of the current ignition cycle. |
| • | A history U1300 will clear upon receipt of a scan tool Clear DTCs
command. |
Diagnostic Aids
| • | This DTC cannot be retrieved with a current status. The diagnosis
of a current U1300 is accomplished via the symptom, Scan Tool Does Not Communicate
with a Class 2 Device. |
| • | An intermittent condition is likely to be caused by a short to
ground on the class 2 serial data circuit. Use the Scan Tool Does Not Communicate
with a Class 2 Device procedure to isolate an intermittent condition. |
