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 circuit about once every two seconds. When the module detects no
messages and a high voltage on the Class 2 serial data circuit for approximately
three seconds, U1301 is set and the setting of all other communication DTCs
is inhibited.
Conditions for Running the DTC
| • | Voltage supplied to the modules are in the normal operating voltage
range (approximately 9-16 volts). |
| • | The vehicle power mode (ignition switch position) requires serial
data communication to occur. |
Conditions for Setting the DTC
| • | No valid Class 2 messages are detected on the Class 2 serial data
circuit. |
| • | The voltage level detected on the Class 2 serial data circuit
is high. |
| • | The above conditions are all 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 U1301 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 U1301 will clear upon receipt of a scan tool CLEAR DTCs
command. |
Diagnostic Aids
| • | This DTC cannot be retrieved with a current status. Diagnosis
of a current U1301 is accomplished via the symptom, Scan Tool Will Not Communicate
With Class 2 Data Line. |
| • | An intermittent condition is likely to be caused by a short to
voltage on the Class 2 serial data circuit. Use the Scan Tool Will Not Communicate
With Class 2 Data Line procedure to isolate the condition. |
